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507122805e
In the work to remove proc_mnt I noticed that we were calling
proc_flush_task now proc_flush_pid possibly multiple times for the same
pid because of how de_thread works.
This is a bare minimal patchset to sort out de_thread, by introducing
exchange_tids and the helper of exchange_tids hlists_swap_heads_rcu.
The actual call of exchange_tids should be slowpath so I have
prioritized readability over getting every last drop of performance.
I have also read through a bunch of the code to see if I could find
anything that would be affected by this change. Users of
has_group_leader_pid were a good canidates. But I also looked at other
cases that might have a pid->task->pid transition. I ignored other
sources of races with de_thread and exec as those are preexisting.
I found a close call with send_signals user of task_active_pid_ns, but
all pids of a thread group are guaranteeds to be in the same pid
namespace so there is not a problem.
I found a few pieces of debugging code that do:
task = pid_task(pid, PIDTYPE_PID);
if (task) {
printk("%u\n", task->pid);
}
But I can't see how we care if it happens at the wrong moment that
task->pid might not match pid_nr(pid);
Similarly because the code in posix-cpu-timers goes pid->task->pid it
feels like there should be a problem. But as the code that works with
PIDTYPE_PID is only available within the thread group, and as de_thread
kills all of the other threads before it makes any changes of this
kind the race can not happen.
In short I don't think this change will introduce any regressions.
Eric W. Biederman (2):
rculist: Add hlists_swap_heads_rcu
proc: Ensure we see the exit of each process tid exactly once
fs/exec.c | 5 +----
include/linux/pid.h | 1 +
include/linux/rculist.h | 21 +++++++++++++++++++++
kernel/pid.c | 19 +++++++++++++++++++
4 files changed, 42 insertions(+), 4 deletions(-)
Link: https://lore.kernel.org/lkml/87sggnajpv.fsf_-_@x220.int.ebiederm.org/
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.