[merged mm-hotfixes-stable] fs-proc-do_task_stat-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch removed from -mm tree

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The quilt patch titled
     Subject: fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task_sighand()
has been removed from the -mm tree.  Its filename was
     fs-proc-do_task_stat-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
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

ptrace_attach-shift-sendsigstop-into-ptrace_set_stopped.patch





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