This is a note to let you know that I've just added the patch titled
fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task_sighand()
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fs-proc-do_task_stat-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 60f92acb60a989b14e4b744501a0df0f82ef30a3 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Date: Tue, 23 Jan 2024 16:33:55 +0100
Subject: fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task_sighand()
From: Oleg Nesterov <oleg@xxxxxxxxxx>
commit 60f92acb60a989b14e4b744501a0df0f82ef30a3 upstream.
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@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20240123153355.GA21854@xxxxxxxxxx
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Dylan Hatch <dylanbhatch@xxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/proc/array.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -501,7 +501,7 @@ 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)) {
@@ -535,7 +535,6 @@ 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))
@@ -551,10 +550,13 @@ 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 stable-queue which might be from oleg@xxxxxxxxxx are
queue-6.1/exit-wait_task_zombie-kill-the-no-longer-necessary-spin_lock_irq-siglock.patch
queue-6.1/fs-proc-do_task_stat-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch
