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Eric W. Biederman 6b03d1304a proc: Ensure we see the exit of each process tid exactly once 
When the thread group leader changes during exec and the old leaders
thread is reaped proc_flush_pid will flush the dentries for the entire
process because the leader still has it's original pid.

Fix this by exchanging the pids in an rcu safe manner,
and wrapping the code to do that up in a helper exchange_tids.

When I removed switch_exec_pids and introduced this behavior
in d73d65293e ("[PATCH] pidhash: kill switch_exec_pids") there
really was nothing that cared as flushing happened with
the cached dentry and de_thread flushed both of them on exec.

This lack of fully exchanging pids became a problem a few months later
when I introduced 48e6484d49 ("[PATCH] proc: Rewrite the proc dentry
flush on exit optimization").  Which overlooked the de_thread case
was no longer swapping pids, and I was looking up proc dentries
by task->pid.

The current behavior isn't properly a bug as everything in proc will
continue to work correctly just a little bit less efficiently.  Fix
this just so there are no little surprise corner cases waiting to bite
people.

-- Oleg points out this could be an issue in next_tgid in proc where
   has_group_leader_pid is called, and reording some of the assignments
   should fix that.

-- Oleg points out this will break the 10 year old hack in __exit_signal.c
>	/*
>	 * This can only happen if the caller is de_thread().
>	 * FIXME: this is the temporary hack, we should teach
>	 * posix-cpu-timers to handle this case correctly.
>	 */
>	if (unlikely(has_group_leader_pid(tsk)))
>		posix_cpu_timers_exit_group(tsk);

The code in next_tgid has been changed to use PIDTYPE_TGID,
and the posix cpu timers code has been fixed so it does not
need the 10 year old hack, so this should be safe to merge
now.

Link: https://lore.kernel.org/lkml/87h7x3ajll.fsf_-_@x220.int.ebiederm.org/
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Fixes: 48e6484d49 ("[PATCH] proc: Rewrite the proc dentry flush on exit optimization").
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
2020-04-28 16:13:58 -05:00
arch A set of three patches to fix the fallout of the newly added split lock 2020-04-12 10:17:16 -07:00
block block-5.7-2020-04-10 2020-04-10 10:06:54 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto x86: update AS_* macros to binutils >=2.23, supporting ADX and AVX2 2020-04-09 00:12:48 +09:00
Documentation proc: use human-readable values for hidepid 2020-04-22 10:51:22 -05:00
drivers Kbuild updates for v5.7 (2nd) 2020-04-11 09:46:12 -07:00
fs proc: Ensure we see the exit of each process tid exactly once 2020-04-28 16:13:58 -05:00
include proc: Ensure we see the exit of each process tid exactly once 2020-04-28 16:13:58 -05:00
init Kbuild updates for v5.7 (2nd) 2020-04-11 09:46:12 -07:00
ipc ipc/util.c: sysvipc_find_ipc() should increase position index 2020-04-10 15:36:22 -07:00
kernel proc: Ensure we see the exit of each process tid exactly once 2020-04-28 16:13:58 -05:00
lib Kbuild updates for v5.7 (2nd) 2020-04-11 09:46:12 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm Merge branch 'akpm' (patches from Andrew) 2020-04-10 17:57:48 -07:00
net Kbuild updates for v5.7 (2nd) 2020-04-11 09:46:12 -07:00
samples samples/hw_breakpoint: drop use of kallsyms_lookup_name() 2020-04-07 10:43:44 -07:00
scripts kbuild: add dummy toolchains to enable all cc-option etc. in Kconfig 2020-04-09 00:13:45 +09:00
security Use proc_pid_ns() to get pid_namespace from the proc superblock 2020-04-24 16:38:30 -05:00
sound sound fixes for 5.7-rc1 2020-04-10 12:27:06 -07:00
tools proc: use human-readable values for hidepid 2020-04-22 10:51:22 -05:00
usr kbuild: fix comment about missing include guard detection 2020-04-11 12:09:48 +09:00
virt KVM: Pass kvm_init()'s opaque param to additional arch funcs 2020-03-31 10:48:03 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2020-03-06 21:50:05 +01:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
.mailmap mailmap: Add Sedat Dilek (replacement for expired email address) 2020-04-11 09:28:34 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Hand MIPS over to Thomas 2020-02-24 22:43:18 -08:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: sort field names for all entries 2020-04-12 11:04:58 -07:00
Makefile Linux 5.7-rc1 2020-04-12 12:35:55 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.