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/fs-proc-do_task_stat-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
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@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>
---
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@xxxxxxxxxx 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
