The patch titled Subject: fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task_sighand() has been added to the -mm mm-hotfixes-unstable branch. Its filename is fs-proc-do_task_stat-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days

------------------------------------------------------ From: Oleg Nesterov oleg@redhat.com Subject: fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task_sighand() Date: Tue, 23 Jan 2024 16:33:55 +0100

Patch series "fs/proc: do_task_stat: use sig->stats_".

do_task_stat() has the same problem as getrusage() had before "getrusage: use sig->stats_lock rather than lock_task_sighand()": a hard lockup. If NR_CPUS threads call lock_task_sighand() at the same time and the process has NR_THREADS, spin_lock_irq will spin with irqs disabled O(NR_CPUS * NR_THREADS) time.

This patch (of 3):

thread_group_cputime() does its own locking, we can safely shift thread_group_cputime_adjusted() which does another for_each_thread loop outside of ->siglock protected section.

Not only this removes for_each_thread() from the critical section with irqs disabled, this removes another case when stats_lock is taken with siglock held. We want to remove this dependency, then we can change the users of stats_lock to not disable irqs.

Link: https://lkml.kernel.org/r/20240123153313.GA21832@redhat.com Link: https://lkml.kernel.org/r/20240123153355.GA21854@redhat.com Signed-off-by: Oleg Nesterov oleg@redhat.com Signed-off-by: Dylan Hatch dylanbhatch@google.com Cc: Eric W. Biederman ebiederm@xmission.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/proc/array.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/fs/proc/array.c~fs-proc-do_task_stat-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand +++ a/fs/proc/array.c @@ -511,7 +511,7 @@ static int do_task_stat(struct seq_file

sigemptyset(&sigign); sigemptyset(&sigcatch); - cutime = cstime = utime = stime = 0; + cutime = cstime = 0; cgtime = gtime = 0;

if (lock_task_sighand(task, &flags)) { @@ -546,7 +546,6 @@ static int do_task_stat(struct seq_file

min_flt += sig->min_flt; maj_flt += sig->maj_flt; - thread_group_cputime_adjusted(task, &utime, &stime); gtime += sig->gtime;

if (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_STOP_STOPPED)) @@ -562,10 +561,13 @@ static int do_task_stat(struct seq_file

if (permitted && (!whole || num_threads < 2)) wchan = !task_is_running(task); - if (!whole) { + + if (whole) { + thread_group_cputime_adjusted(task, &utime, &stime); + } else { + task_cputime_adjusted(task, &utime, &stime); min_flt = task->min_flt; maj_flt = task->maj_flt; - task_cputime_adjusted(task, &utime, &stime); gtime = task_gtime(task); }

_

Patches currently in -mm which might be from oleg@redhat.com are

getrusage-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch getrusage-use-sig-stats_lock-rather-than-lock_task_sighand.patch fs-proc-do_task_stat-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch fs-proc-do_task_stat-use-sig-stats_lock-to-gather-the-threads-children-stats.patch exit-wait_task_zombie-kill-the-no-longer-necessary-spin_lock_irqsiglock.patch ptrace_attach-shift-sendsigstop-into-ptrace_set_stopped.patch