For historical reasons mips has to override the socket enum values but
the defines are all the same. So simply move the ARCH_HAS_SOCKET_TYPES
scope.
Fixes: a9194f8878 ("coredump: add coredump socket")
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Christian Brauner <brauner@kernel.org> says:
Coredumping currently supports two modes:
(1) Dumping directly into a file somewhere on the filesystem.
(2) Dumping into a pipe connected to a usermode helper process
spawned as a child of the system_unbound_wq or kthreadd.
For simplicity I'm mostly ignoring (1). There's probably still some
users of (1) out there but processing coredumps in this way can be
considered adventurous especially in the face of set*id binaries.
The most common option should be (2) by now. It works by allowing
userspace to put a string into /proc/sys/kernel/core_pattern like:
|/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h
The "|" at the beginning indicates to the kernel that a pipe must be
used. The path following the pipe indicator is a path to a binary that
will be spawned as a usermode helper process. Any additional parameters
pass information about the task that is generating the coredump to the
binary that processes the coredump.
In the example core_pattern shown above systemd-coredump is spawned as a
usermode helper. There's various conceptual consequences of this
(non-exhaustive list):
- systemd-coredump is spawned with file descriptor number 0 (stdin)
connected to the read-end of the pipe. All other file descriptors are
closed. That specifically includes 1 (stdout) and 2 (stderr). This has
already caused bugs because userspace assumed that this cannot happen
(Whether or not this is a sane assumption is irrelevant.).
- systemd-coredump will be spawned as a child of system_unbound_wq. So
it is not a child of any userspace process and specifically not a
child of PID 1. It cannot be waited upon and is in a weird hybrid
upcall which are difficult for userspace to control correctly.
- systemd-coredump is spawned with full kernel privileges. This
necessitates all kinds of weird privilege dropping excercises in
userspace to make this safe.
- A new usermode helper has to be spawned for each crashing process.
This series adds a new mode:
(3) Dumping into an AF_UNIX socket.
Userspace can set /proc/sys/kernel/core_pattern to:
@/path/to/coredump.socket
The "@" at the beginning indicates to the kernel that an AF_UNIX
coredump socket will be used to process coredumps.
The coredump socket must be located in the initial mount namespace.
When a task coredumps it opens a client socket in the initial network
namespace and connects to the coredump socket.
- The coredump server should use SO_PEERPIDFD to get a stable handle on
the connected crashing task. The retrieved pidfd will provide a stable
reference even if the crashing task gets SIGKILLed while generating
the coredump.
- By setting core_pipe_limit non-zero userspace can guarantee that the
crashing task cannot be reaped behind it's back and thus process all
necessary information in /proc/<pid>. The SO_PEERPIDFD can be used to
detect whether /proc/<pid> still refers to the same process.
The core_pipe_limit isn't used to rate-limit connections to the
socket. This can simply be done via AF_UNIX socket directly.
- The pidfd for the crashing task will contain information how the task
coredumps. The PIDFD_GET_INFO ioctl gained a new flag
PIDFD_INFO_COREDUMP which can be used to retreive the coredump
information.
If the coredump gets a new coredump client connection the kernel
guarantees that PIDFD_INFO_COREDUMP information is available.
Currently the following information is provided in the new
@coredump_mask extension to struct pidfd_info:
* PIDFD_COREDUMPED is raised if the task did actually coredump.
* PIDFD_COREDUMP_SKIP is raised if the task skipped coredumping (e.g.,
undumpable).
* PIDFD_COREDUMP_USER is raised if this is a regular coredump and
doesn't need special care by the coredump server.
* PIDFD_COREDUMP_ROOT is raised if the generated coredump should be
treated as sensitive and the coredump server should restrict access
to the generated coredump to sufficiently privileged users.
- The coredump server should mark itself as non-dumpable.
- A container coredump server in a separate network namespace can simply
bind to another well-know address and systemd-coredump fowards
coredumps to the container.
- Coredumps could in the future also be handled via per-user/session
coredump servers that run only with that users privileges.
The coredump server listens on the coredump socket and accepts a
new coredump connection. It then retrieves SO_PEERPIDFD for the
client, inspects uid/gid and hands the accepted client to the users
own coredump handler which runs with the users privileges only
(It must of coure pay close attention to not forward crashing suid
binaries.).
The new coredump socket will allow userspace to not have to rely on
usermode helpers for processing coredumps and provides a safer way to
handle them instead of relying on super privileged coredumping helpers.
This will also be significantly more lightweight since no fork()+exec()
for the usermodehelper is required for each crashing process. The
coredump server in userspace can just keep a worker pool.
* patches from https://lore.kernel.org/20250516-work-coredump-socket-v8-0-664f3caf2516@kernel.org:
selftests/coredump: add tests for AF_UNIX coredumps
selftests/pidfd: add PIDFD_INFO_COREDUMP infrastructure
coredump: validate socket name as it is written
coredump: show supported coredump modes
pidfs, coredump: add PIDFD_INFO_COREDUMP
coredump: add coredump socket
coredump: reflow dump helpers a little
coredump: massage do_coredump()
coredump: massage format_corename()
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-0-664f3caf2516@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Add a simple test for generating coredumps via AF_UNIX sockets.
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-9-664f3caf2516@kernel.org
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Add PIDFD_INFO_COREDUMP infrastructure so we can use it in tests.
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-8-664f3caf2516@kernel.org
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
In contrast to other parameters written into
/proc/sys/kernel/core_pattern that never fail we can validate enabling
the new AF_UNIX support. This is obviously racy as hell but it's always
been that way.
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-7-664f3caf2516@kernel.org
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Extend the PIDFD_INFO_COREDUMP ioctl() with the new PIDFD_INFO_COREDUMP
mask flag. This adds the @coredump_mask field to struct pidfd_info.
When a task coredumps the kernel will provide the following information
to userspace in @coredump_mask:
* PIDFD_COREDUMPED is raised if the task did actually coredump.
* PIDFD_COREDUMP_SKIP is raised if the task skipped coredumping (e.g.,
undumpable).
* PIDFD_COREDUMP_USER is raised if this is a regular coredump and
doesn't need special care by the coredump server.
* PIDFD_COREDUMP_ROOT is raised if the generated coredump should be
treated as sensitive and the coredump server should restrict to the
generated coredump to sufficiently privileged users.
The kernel guarantees that by the time the connection is made the all
PIDFD_INFO_COREDUMP info is available.
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-5-664f3caf2516@kernel.org
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Coredumping currently supports two modes:
(1) Dumping directly into a file somewhere on the filesystem.
(2) Dumping into a pipe connected to a usermode helper process
spawned as a child of the system_unbound_wq or kthreadd.
For simplicity I'm mostly ignoring (1). There's probably still some
users of (1) out there but processing coredumps in this way can be
considered adventurous especially in the face of set*id binaries.
The most common option should be (2) by now. It works by allowing
userspace to put a string into /proc/sys/kernel/core_pattern like:
|/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h
The "|" at the beginning indicates to the kernel that a pipe must be
used. The path following the pipe indicator is a path to a binary that
will be spawned as a usermode helper process. Any additional parameters
pass information about the task that is generating the coredump to the
binary that processes the coredump.
In the example core_pattern shown above systemd-coredump is spawned as a
usermode helper. There's various conceptual consequences of this
(non-exhaustive list):
- systemd-coredump is spawned with file descriptor number 0 (stdin)
connected to the read-end of the pipe. All other file descriptors are
closed. That specifically includes 1 (stdout) and 2 (stderr). This has
already caused bugs because userspace assumed that this cannot happen
(Whether or not this is a sane assumption is irrelevant.).
- systemd-coredump will be spawned as a child of system_unbound_wq. So
it is not a child of any userspace process and specifically not a
child of PID 1. It cannot be waited upon and is in a weird hybrid
upcall which are difficult for userspace to control correctly.
- systemd-coredump is spawned with full kernel privileges. This
necessitates all kinds of weird privilege dropping excercises in
userspace to make this safe.
- A new usermode helper has to be spawned for each crashing process.
This series adds a new mode:
(3) Dumping into an AF_UNIX socket.
Userspace can set /proc/sys/kernel/core_pattern to:
@/path/to/coredump.socket
The "@" at the beginning indicates to the kernel that an AF_UNIX
coredump socket will be used to process coredumps.
The coredump socket must be located in the initial mount namespace.
When a task coredumps it opens a client socket in the initial network
namespace and connects to the coredump socket.
- The coredump server uses SO_PEERPIDFD to get a stable handle on the
connected crashing task. The retrieved pidfd will provide a stable
reference even if the crashing task gets SIGKILLed while generating
the coredump.
- By setting core_pipe_limit non-zero userspace can guarantee that the
crashing task cannot be reaped behind it's back and thus process all
necessary information in /proc/<pid>. The SO_PEERPIDFD can be used to
detect whether /proc/<pid> still refers to the same process.
The core_pipe_limit isn't used to rate-limit connections to the
socket. This can simply be done via AF_UNIX sockets directly.
- The pidfd for the crashing task will grow new information how the task
coredumps.
- The coredump server should mark itself as non-dumpable.
- A container coredump server in a separate network namespace can simply
bind to another well-know address and systemd-coredump fowards
coredumps to the container.
- Coredumps could in the future also be handled via per-user/session
coredump servers that run only with that users privileges.
The coredump server listens on the coredump socket and accepts a
new coredump connection. It then retrieves SO_PEERPIDFD for the
client, inspects uid/gid and hands the accepted client to the users
own coredump handler which runs with the users privileges only
(It must of coure pay close attention to not forward crashing suid
binaries.).
The new coredump socket will allow userspace to not have to rely on
usermode helpers for processing coredumps and provides a safer way to
handle them instead of relying on super privileged coredumping helpers
that have and continue to cause significant CVEs.
This will also be significantly more lightweight since no fork()+exec()
for the usermodehelper is required for each crashing process. The
coredump server in userspace can e.g., just keep a worker pool.
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-4-664f3caf2516@kernel.org
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
They look rather messy right now.
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-3-664f3caf2516@kernel.org
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
We're going to extend the coredump code in follow-up patches.
Clean it up so we can do this more easily.
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-2-664f3caf2516@kernel.org
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
We're going to extend the coredump code in follow-up patches.
Clean it up so we can do this more easily.
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-1-664f3caf2516@kernel.org
Acked-by: Serge Hallyn <serge@hallyn.com>
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Christian Brauner <brauner@kernel.org> says:
Give userspace a way to instruct the kernel to install a pidfd for the
crashing process into the process started as a usermode helper. There's
still tricky race-windows that cannot be easily or sometimes not closed
at all by userspace. There's various ways like looking at the start time
of a process to make sure that the usermode helper process is started
after the crashing process but it's all very very brittle and fraught
with peril.
The crashed-but-not-reaped process can be killed by userspace before
coredump processing programs like systemd-coredump have had time to
manually open a PIDFD from the PID the kernel provides them, which means
they can be tricked into reading from an arbitrary process, and they run
with full privileges as they are usermode helper processes.
Even if that specific race-window wouldn't exist it's still the safest
and cleanest way to let the kernel provide the pidfd directly instead of
requiring userspace to do it manually. In parallel with this commit we
already have systemd adding support for this in [1].
When the usermode helper process is forked we install a pidfd file
descriptor three into the usermode helper's file descriptor table so
it's available to the exec'd program.
Since usermode helpers are either children of the system_unbound_wq
workqueue or kthreadd we know that the file descriptor table is empty
and can thus always use three as the file descriptor number.
Note, that we'll install a pidfd for the thread-group leader even if a
subthread is calling do_coredump(). We know that task linkage hasn't
been removed yet and even if this @current isn't the actual thread-group
leader we know that the thread-group leader cannot be reaped until
@current has exited.
[1]: https://github.com/systemd/systemd/pull/37125
* patches from https://lore.kernel.org/20250414-work-coredump-v2-0-685bf231f828@kernel.org:
coredump: hand a pidfd to the usermode coredump helper
coredump: fix error handling for replace_fd()
pidfs: move O_RDWR into pidfs_alloc_file()
Link: https://lore.kernel.org/20250414-work-coredump-v2-0-685bf231f828@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Give userspace a way to instruct the kernel to install a pidfd into the
usermode helper process. This makes coredump handling a lot more
reliable for userspace. In parallel with this commit we already have
systemd adding support for this in [1].
We create a pidfs file for the coredumping process when we process the
corename pattern. When the usermode helper process is forked we then
install the pidfs file as file descriptor three into the usermode
helpers file descriptor table so it's available to the exec'd program.
Since usermode helpers are either children of the system_unbound_wq
workqueue or kthreadd we know that the file descriptor table is empty
and can thus always use three as the file descriptor number.
Note, that we'll install a pidfd for the thread-group leader even if a
subthread is calling do_coredump(). We know that task linkage hasn't
been removed due to delay_group_leader() and even if this @current isn't
the actual thread-group leader we know that the thread-group leader
cannot be reaped until @current has exited.
Link: https://github.com/systemd/systemd/pull/37125 [1]
Link: https://lore.kernel.org/20250414-work-coredump-v2-3-685bf231f828@kernel.org
Tested-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
The replace_fd() helper returns the file descriptor number on success
and a negative error code on failure. The current error handling in
umh_pipe_setup() only works because the file descriptor that is replaced
is zero but that's pretty volatile. Explicitly check for a negative
error code.
Link: https://lore.kernel.org/20250414-work-coredump-v2-2-685bf231f828@kernel.org
Tested-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Since all pidfds must be O_RDWR currently enfore that directly in the
file allocation function itself instead of letting callers specify it.
Link: https://lore.kernel.org/20250414-work-coredump-v2-1-685bf231f828@kernel.org
Tested-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Nam Cao <namcao@linutronix.de> says:
While trying the coredump test on qemu-system-riscv64, I observed test
failures for various reasons.
This series makes the test works on qemu-system-riscv64.
* patches from https://lore.kernel.org/cover.1744383419.git.namcao@linutronix.de:
selftests: coredump: Raise timeout to 2 minutes
selftests: coredump: Fix test failure for slow machines
selftests: coredump: Properly initialize pointer
Link: https://lore.kernel.org/cover.1744383419.git.namcao@linutronix.de
Signed-off-by: Christian Brauner <brauner@kernel.org>
The test's runtime (nearly 20s) is dangerously close to the limit (30s) on
qemu-system-riscv64:
$ time ./stackdump_test > /dev/null
real 0m19.210s
user 0m0.077s
sys 0m0.359s
There could be machines slower than qemu-system-riscv64. Therefore raise
the test timeout to 2 minutes to be safe.
Fixes: 15858da535 ("selftests: coredump: Add stackdump test")
Signed-off-by: Nam Cao <namcao@linutronix.de>
Link: https://lore.kernel.org/dd636084d55e7828782728d087fa2298dcab1c8b.1744383419.git.namcao@linutronix.de
Signed-off-by: Christian Brauner <brauner@kernel.org>
The test waits for coredump to finish by busy-waiting for the stack_values
file to be created. The maximum wait time is 10 seconds.
This doesn't work for slow machine (qemu-system-riscv64), because coredump
takes longer.
Fix it by waiting for the crashing child process to finish first.
Fixes: 15858da535 ("selftests: coredump: Add stackdump test")
Signed-off-by: Nam Cao <namcao@linutronix.de>
Link: https://lore.kernel.org/ee657f3fc8e19657cf7aaa366552d6347728f371.1744383419.git.namcao@linutronix.de
Signed-off-by: Christian Brauner <brauner@kernel.org>
The buffer pointer "line" is not initialized. This pointer is passed to
getline().
It can still work if the stack is zero-initialized, because getline() can
work with a NULL pointer as buffer.
But this is obviously broken. This bug shows up while running the test on a
riscv64 machine.
Fix it by properly initializing the pointer.
Fixes: 15858da535 ("selftests: coredump: Add stackdump test")
Signed-off-by: Nam Cao <namcao@linutronix.de>
Link: https://lore.kernel.org/4fb9b6fb3e0040481bacc258c44b4aab5c4df35d.1744383419.git.namcao@linutronix.de
Signed-off-by: Christian Brauner <brauner@kernel.org>
Christian Brauner <brauner@kernel.org> says:
SO_PEERPIDFD currently doesn't support handing out pidfds if the
sk->sk_peer_pid thread-group leader has already been reaped. In this
case it currently returns EINVAL. Userspace still wants to get a pidfd
for a reaped process to have a stable handle it can pass on.
This is especially useful now that it is possible to retrieve exit
information through a pidfd via the PIDFD_GET_INFO ioctl()'s
PIDFD_INFO_EXIT flag.
Another summary has been provided by David in [1]:
> A pidfd can outlive the task it refers to, and thus user-space must
> already be prepared that the task underlying a pidfd is gone at the time
> they get their hands on the pidfd. For instance, resolving the pidfd to
> a PID via the fdinfo must be prepared to read `-1`.
>
> Despite user-space knowing that a pidfd might be stale, several kernel
> APIs currently add another layer that checks for this. In particular,
> SO_PEERPIDFD returns `EINVAL` if the peer-task was already reaped,
> but returns a stale pidfd if the task is reaped immediately after the
> respective alive-check.
>
> This has the unfortunate effect that user-space now has two ways to
> check for the exact same scenario: A syscall might return
> EINVAL/ESRCH/... *or* the pidfd might be stale, even though there is no
> particular reason to distinguish both cases. This also propagates
> through user-space APIs, which pass on pidfds. They must be prepared to
> pass on `-1` *or* the pidfd, because there is no guaranteed way to get a
> stale pidfd from the kernel.
> Userspace must already deal with a pidfd referring to a reaped task as
> the task may exit and get reaped at any time will there are still many
> pidfds referring to it.
In order to allow handing out reaped pidfd SO_PEERPIDFD needs to ensure
that PIDFD_INFO_EXIT information is available whenever a pidfd for a
reaped task is created by PIDFD_INFO_EXIT. The uapi promises that reaped
pidfds are only handed out if it is guaranteed that the caller sees the
exit information:
TEST_F(pidfd_info, success_reaped)
{
struct pidfd_info info = {
.mask = PIDFD_INFO_CGROUPID | PIDFD_INFO_EXIT,
};
/*
* Process has already been reaped and PIDFD_INFO_EXIT been set.
* Verify that we can retrieve the exit status of the process.
*/
ASSERT_EQ(ioctl(self->child_pidfd4, PIDFD_GET_INFO, &info), 0);
ASSERT_FALSE(!!(info.mask & PIDFD_INFO_CREDS));
ASSERT_TRUE(!!(info.mask & PIDFD_INFO_EXIT));
ASSERT_TRUE(WIFEXITED(info.exit_code));
ASSERT_EQ(WEXITSTATUS(info.exit_code), 0);
}
To hand out pidfds for reaped processes we thus allocate a pidfs entry
for the relevant sk->sk_peer_pid at the time the sk->sk_peer_pid is
stashed and drop it when the socket is destroyed. This guarantees that
exit information will always be recorded for the sk->sk_peer_pid task
and we can hand out pidfds for reaped processes.
* patches from https://lore.kernel.org/20250425-work-pidfs-net-v2-0-450a19461e75@kernel.org:
net, pidfs: enable handing out pidfds for reaped sk->sk_peer_pid
pidfs: get rid of __pidfd_prepare()
net, pidfs: prepare for handing out pidfds for reaped sk->sk_peer_pid
pidfs: register pid in pidfs
Link: https://lore.kernel.org/20250425-work-pidfs-net-v2-0-450a19461e75@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Now that all preconditions are met, allow handing out pidfs for reaped
sk->sk_peer_pids.
Thanks to Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
for pointing out that we need to limit this to AF_UNIX sockets for now.
Link: https://lore.kernel.org/20250425-work-pidfs-net-v2-4-450a19461e75@kernel.org
Reviewed-by: David Rheinsberg <david@readahead.eu>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Fold it into pidfd_prepare() and rename PIDFD_CLONE to PIDFD_STALE to
indicate that the passed pid might not have task linkage and no explicit
check for that should be performed.
Link: https://lore.kernel.org/20250425-work-pidfs-net-v2-3-450a19461e75@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: David Rheinsberg <david@readahead.eu>
Signed-off-by: Christian Brauner <brauner@kernel.org>
SO_PEERPIDFD currently doesn't support handing out pidfds if the
sk->sk_peer_pid thread-group leader has already been reaped. In this
case it currently returns EINVAL. Userspace still wants to get a pidfd
for a reaped process to have a stable handle it can pass on.
This is especially useful now that it is possible to retrieve exit
information through a pidfd via the PIDFD_GET_INFO ioctl()'s
PIDFD_INFO_EXIT flag.
Another summary has been provided by David in [1]:
> A pidfd can outlive the task it refers to, and thus user-space must
> already be prepared that the task underlying a pidfd is gone at the time
> they get their hands on the pidfd. For instance, resolving the pidfd to
> a PID via the fdinfo must be prepared to read `-1`.
>
> Despite user-space knowing that a pidfd might be stale, several kernel
> APIs currently add another layer that checks for this. In particular,
> SO_PEERPIDFD returns `EINVAL` if the peer-task was already reaped,
> but returns a stale pidfd if the task is reaped immediately after the
> respective alive-check.
>
> This has the unfortunate effect that user-space now has two ways to
> check for the exact same scenario: A syscall might return
> EINVAL/ESRCH/... *or* the pidfd might be stale, even though there is no
> particular reason to distinguish both cases. This also propagates
> through user-space APIs, which pass on pidfds. They must be prepared to
> pass on `-1` *or* the pidfd, because there is no guaranteed way to get a
> stale pidfd from the kernel.
> Userspace must already deal with a pidfd referring to a reaped task as
> the task may exit and get reaped at any time will there are still many
> pidfds referring to it.
In order to allow handing out reaped pidfd SO_PEERPIDFD needs to ensure
that PIDFD_INFO_EXIT information is available whenever a pidfd for a
reaped task is created by PIDFD_INFO_EXIT. The uapi promises that reaped
pidfds are only handed out if it is guaranteed that the caller sees the
exit information:
TEST_F(pidfd_info, success_reaped)
{
struct pidfd_info info = {
.mask = PIDFD_INFO_CGROUPID | PIDFD_INFO_EXIT,
};
/*
* Process has already been reaped and PIDFD_INFO_EXIT been set.
* Verify that we can retrieve the exit status of the process.
*/
ASSERT_EQ(ioctl(self->child_pidfd4, PIDFD_GET_INFO, &info), 0);
ASSERT_FALSE(!!(info.mask & PIDFD_INFO_CREDS));
ASSERT_TRUE(!!(info.mask & PIDFD_INFO_EXIT));
ASSERT_TRUE(WIFEXITED(info.exit_code));
ASSERT_EQ(WEXITSTATUS(info.exit_code), 0);
}
To hand out pidfds for reaped processes we thus allocate a pidfs entry
for the relevant sk->sk_peer_pid at the time the sk->sk_peer_pid is
stashed and drop it when the socket is destroyed. This guarantees that
exit information will always be recorded for the sk->sk_peer_pid task
and we can hand out pidfds for reaped processes.
Link: https://lore.kernel.org/lkml/20230807085203.819772-1-david@readahead.eu [1]
Link: https://lore.kernel.org/20250425-work-pidfs-net-v2-2-450a19461e75@kernel.org
Reviewed-by: David Rheinsberg <david@readahead.eu>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Add simple helpers that allow a struct pid to be pinned via a pidfs
dentry/inode. If no pidfs dentry exists a new one will be allocated for
it. A reference is taken by pidfs on @pid. The reference must be
released via pidfs_put_pid().
This will allow AF_UNIX sockets to allocate a dentry for the peer
credentials pid at the time they are recorded where we know the task is
still alive. When the task gets reaped its exit status is guaranteed to
be recorded and a pidfd can be handed out for the reaped task.
Link: https://lore.kernel.org/20250425-work-pidfs-net-v2-1-450a19461e75@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: David Rheinsberg <david@readahead.eu>
Signed-off-by: Christian Brauner <brauner@kernel.org>
After the commit 7903f907a2 ("pid: perform free_pid() calls outside
of tasklist_lock") __unhash_process() -> detach_pid() no longer calls
free_pid(), proc_flush_pid() can just use p->thread_pid without the
now pointless get_pid() + put_pid().
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/20250411121857.GA10550@redhat.com
Reviewed-by: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Christian Brauner <brauner@kernel.org> says:
In a prior patch series we tried to cleanly differentiate between:
(1) The task has already been reaped.
(2) The caller requested a pidfd for a thread-group leader but the pid
actually references a struct pid that isn't used as a thread-group
leader.
as this was causing issues for non-threaded workloads.
But there's cases where the current simple logic is wrong. Specifically,
if the pid was a leader pid and the check races with __unhash_process().
Stabilize this by using the pidfd waitqueue lock.
* patches from https://lore.kernel.org/20250411-work-pidfs-enoent-v2-0-60b2d3bb545f@kernel.org:
pidfs: ensure consistent ENOENT/ESRCH reporting
exit: move wake_up_all() pidfd waiters into __unhash_process()
Link: https://lore.kernel.org/20250411-work-pidfs-enoent-v2-0-60b2d3bb545f@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
In a prior patch series we tried to cleanly differentiate between:
(1) The task has already been reaped.
(2) The caller requested a pidfd for a thread-group leader but the pid
actually references a struct pid that isn't used as a thread-group
leader.
as this was causing issues for non-threaded workloads.
But there's cases where the current simple logic is wrong. Specifically,
if the pid was a leader pid and the check races with __unhash_process().
Stabilize this by using the pidfd waitqueue lock.
Link: https://lore.kernel.org/20250411-work-pidfs-enoent-v2-2-60b2d3bb545f@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Move the pidfd notification out of __change_pid() and into
__unhash_process(). The only valid call to __change_pid() with a NULL
argument and PIDTYPE_PID is from __unhash_process(). This is a lot more
obvious than calling it from __change_pid().
Link: https://lore.kernel.org/20250411-work-pidfs-enoent-v2-1-60b2d3bb545f@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Christian Brauner <brauner@kernel.org> says:
We currently report EINVAL whenever a struct pid has no tasked attached
anymore thereby conflating two concepts:
(1) The task has already been reaped.
(2) The caller requested a pidfd for a thread-group leader but the pid
actually references a struct pid that isn't used as a thread-group
leader.
This is causing issues for non-threaded workloads as in [1] where they
expect ESRCH to be reported, not EINVAL. I think that's a very resonable
assumption.
This patch tries to allow userspace to distinguish between (1) and (2).
This is racy of course but that shouldn't matter.
* patches from https://lore.kernel.org/r/20250403-work-pidfd-fixes-v1-0-a123b6ed6716@kernel.org:
selftest/pidfd: add test for thread-group leader pidfd open for thread
pidfd: improve uapi when task isn't found
pidfd: remove unneeded NULL check from pidfd_prepare()
selftests/pidfd: adapt to recent changes
Link: https://lore.kernel.org/r/20250403-work-pidfd-fixes-v1-0-a123b6ed6716@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Verify that we report ENOENT when userspace tries to create a
thread-group leader pidfd for a thread pidfd that isn't a thread-group
leader.
Link: https://lore.kernel.org/r/20250403-work-pidfd-fixes-v1-4-a123b6ed6716@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
We currently report EINVAL whenever a struct pid has no tasked attached
anymore thereby conflating two concepts:
(1) The task has already been reaped.
(2) The caller requested a pidfd for a thread-group leader but the pid
actually references a struct pid that isn't used as a thread-group
leader.
This is causing issues for non-threaded workloads as in [1].
This patch tries to allow userspace to distinguish between (1) and (2).
This is racy of course but that shouldn't matter.
Link: https://github.com/systemd/systemd/pull/36982 [1]
Link: https://lore.kernel.org/r/20250403-work-pidfd-fixes-v1-3-a123b6ed6716@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Adapt to changes in commit 9133607de3 ("exit: fix the usage of
delay_group_leader->exit_code in do_notify_parent() and pidfs_exit()").
Even if the thread-group leader exited early and succesfully it's exit
status will only be reported once the whole thread-group has exited and
it will share the exit code of the thread-group. So if the thread-group
was SIGKILLed the thread-group leader will also be reported as having
been SIGKILLed.
Link: https://lore.kernel.org/r/20250403-work-pidfd-fixes-v1-1-a123b6ed6716@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
The "real" linux/types.h UAPI header gracefully degrades to a NOOP when
included from assembly code.
Mirror this behaviour in the tools/ variant.
Test for __ASSEMBLER__ over __ASSEMBLY__ as the former is provided by the
toolchain automatically.
Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://lore.kernel.org/lkml/af553c62-ca2f-4956-932c-dd6e3a126f58@sirena.org.uk/
Fixes: c9fbaa8795 ("selftests: vDSO: parse_vdso: Use UAPI headers instead of libc headers")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Link: https://patch.msgid.link/20250321-uapi-consistency-v1-1-439070118dc0@linutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Support up to 8192 processors
Add cpuidle governor debug telemetry, disabled by default
Update default output to exclude cpuidle invocation counts
Bug fixes
Signed-off-by: Len Brown <len.brown@intel.com>
Create "pct_idle" counter group, the sofware notion of residency
so it can now be singled out, independent of other counter groups.
Create "cpuidle" group, the cpuidle invocation counts.
Disable "cpuidle", by default.
Create "swidle" = "cpuidle" + "pct_idle".
Undocument "sysfs", the old name for "swidle", but keep it working
for backwards compatibilty.
Create "hwidle", all the HW idle counters
Modify "idle", enabled by default
"idle" = "hwidle" + "pct_idle" (and now excludes "cpuidle")
Signed-off-by: Len Brown <len.brown@intel.com>
... and don't error out so hard on missing module descriptions.
Before commit 6c6c1fc09d ("modpost: require a MODULE_DESCRIPTION()")
we used to warn about missing module descriptions, but only when
building with extra warnigns (ie 'W=1').
After that commit the warning became an unconditional hard error.
And it turns out not all modules have been converted despite the claims
to the contrary. As reported by Damian Tometzki, the slub KUnit test
didn't have a module description, and apparently nobody ever really
noticed.
The reason nobody noticed seems to be that the slub KUnit tests get
disabled by SLUB_TINY, which also ends up disabling a lot of other code,
both in tests and in slub itself. And so anybody doing full build tests
didn't actually see this failre.
So let's disable SLUB_TINY for build-only tests, since it clearly ends
up limiting build coverage. Also turn the missing module descriptions
error back into a warning, but let's keep it around for non-'W=1'
builds.
Reported-by: Damian Tometzki <damian@riscv-rocks.de>
Link: https://lore.kernel.org/all/01070196099fd059-e8463438-7b1b-4ec8-816d-173874be9966-000000@eu-central-1.amazonses.com/
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Jeff Johnson <jeff.johnson@oss.qualcomm.com>
Fixes: 6c6c1fc09d ("modpost: require a MODULE_DESCRIPTION()")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Probe cpuidle "sysfs" residency and counts separately,
since soon we will make one disabled on, and the
other disabled off.
Clarify that some BIC (build-in-counters) are actually "groups".
since we're about to re-name some of those groups.
no functional change.
Signed-off-by: Len Brown <len.brown@intel.com>
Do fflush() to discard the buffered data, before each read of the
graphics sysfs knobs.
Fixes: ba99a4fc8c ("tools/power turbostat: Remove unnecessary fflush() call")
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Document that on Intel Granite Rapids Systems,
Uncore domains 0-2 are CPU domains, and
uncore domains 3-4 are IO domains.
Signed-off-by: Len Brown <len.brown@intel.com>
The CoreThr column displays total thermal throttling events
since boot time.
Change it to report events during the measurement interval.
This is more useful for showing a user the current conditions.
Total events since boot time are still available to the user via
/sys/devices/system/cpu/cpu*/thermal_throttle/*
Document CoreThr on turbostat.8
Fixes: eae97e053f ("turbostat: Support thermal throttle count print")
Reported-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Cc: Chen Yu <yu.c.chen@intel.com>
On systems with >= 1024 cpus (in my case 1152), turbostat fails with the error output:
"turbostat: /sys/fs/cgroup/cpuset.cpus.effective: cpu str malformat 0-1151"
A similar error appears with the use of turbostat --cpu when the inputted cpu
range contains a cpu number >= 1024:
# turbostat -c 1100-1151
"--cpu 1100-1151" malformed
...
Both errors are caused by parse_cpu_str() reaching its limit of CPU_SUBSET_MAXCPUS.
It's a good idea to limit the maximum cpu number being parsed, but 1024 is too low.
For a small increase in compute and allocated memory, increasing CPU_SUBSET_MAXCPUS
brings support for parsing cpu numbers >= 1024.
Increase CPU_SUBSET_MAXCPUS to 8192, a common setting for CONFIG_NR_CPUS on x86_64.
Signed-off-by: Justin Ernst <justin.ernst@hpe.com>
Signed-off-by: Len Brown <len.brown@intel.com>
1) Convert all del_timer[_sync]() instances over to the new
timer_delete[_sync]() API and remove the legacy wrappers.
Conversion was done with coccinelle plus some manual fixups as
coccinelle chokes on scoped_guard().
2) The final cleanup of the hrtimer_init() to hrtimer_setup() conversion.
This has been delayed to the end of the merge window, so that all
patches which have been merged through other trees are in mainline and
all new users are catched.
Doing this right before rc1 ensures that new code which is merged post rc1
is not introducing new instances of the original functionality.
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Merge tag 'timers-cleanups-2025-04-06' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer cleanups from Thomas Gleixner:
"A set of final cleanups for the timer subsystem:
- Convert all del_timer[_sync]() instances over to the new
timer_delete[_sync]() API and remove the legacy wrappers.
Conversion was done with coccinelle plus some manual fixups as
coccinelle chokes on scoped_guard().
- The final cleanup of the hrtimer_init() to hrtimer_setup()
conversion.
This has been delayed to the end of the merge window, so that all
patches which have been merged through other trees are in mainline
and all new users are catched.
Doing this right before rc1 ensures that new code which is merged post
rc1 is not introducing new instances of the original functionality"
* tag 'timers-cleanups-2025-04-06' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
tracing/timers: Rename the hrtimer_init event to hrtimer_setup
hrtimers: Rename debug_init_on_stack() to debug_setup_on_stack()
hrtimers: Rename debug_init() to debug_setup()
hrtimers: Rename __hrtimer_init_sleeper() to __hrtimer_setup_sleeper()
hrtimers: Remove unnecessary NULL check in hrtimer_start_range_ns()
hrtimers: Make callback function pointer private
hrtimers: Merge __hrtimer_init() into __hrtimer_setup()
hrtimers: Switch to use __htimer_setup()
hrtimers: Delete hrtimer_init()
treewide: Convert new and leftover hrtimer_init() users
treewide: Switch/rename to timer_delete[_sync]()
1) A treewide cleanup for the irq_domain code, which makes the naming
consistent and gets rid of the original oddity of naming domains
'host'.
This is a trivial mechanical change and is done late to ensure that
all instances have been catched and new code merged post rc1 wont
reintroduce new instances.
2) A trivial consistency fix in the migration code
The recent introduction of irq_force_complete_move() in the core
code, causes a problem for the nostalgia crowd who maintains ia64 out
of tree.
The code assumes that hierarchical interrupt domains are enabled and
dereferences irq_data::parent_data unconditionally. That works in mainline
because both architectures which enable that code have hierarchical domains
enabled. Though it breaks the ia64 build, which enables the functionality,
but does not have hierarchical domains.
While it's not really a problem for mainline today, this
unconditional dereference is inconsistent and trivially fixable by
using the existing helper function irqd_get_parent_data(), which has
the appropriate #ifdeffery in place.
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Merge tag 'irq-urgent-2025-04-06' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull more irq updates from Thomas Gleixner:
"A set of updates for the interrupt subsystem:
- A treewide cleanup for the irq_domain code, which makes the naming
consistent and gets rid of the original oddity of naming domains
'host'.
This is a trivial mechanical change and is done late to ensure that
all instances have been catched and new code merged post rc1 wont
reintroduce new instances.
- A trivial consistency fix in the migration code
The recent introduction of irq_force_complete_move() in the core
code, causes a problem for the nostalgia crowd who maintains ia64
out of tree.
The code assumes that hierarchical interrupt domains are enabled
and dereferences irq_data::parent_data unconditionally. That works
in mainline because both architectures which enable that code have
hierarchical domains enabled. Though it breaks the ia64 build,
which enables the functionality, but does not have hierarchical
domains.
While it's not really a problem for mainline today, this
unconditional dereference is inconsistent and trivially fixable by
using the existing helper function irqd_get_parent_data(), which
has the appropriate #ifdeffery in place"
* tag 'irq-urgent-2025-04-06' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
genirq/migration: Use irqd_get_parent_data() in irq_force_complete_move()
irqdomain: Stop using 'host' for domain
irqdomain: Rename irq_get_default_host() to irq_get_default_domain()
irqdomain: Rename irq_set_default_host() to irq_set_default_domain()
