lkml.org 
[lkml]   [2024]   [Mar]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 5.15 65/76] fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task_sighand()
Date
From: Oleg Nesterov <oleg@redhat.com>

[ Upstream commit 60f92acb60a989b14e4b744501a0df0f82ef30a3 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/proc/array.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 77cf4187adecc..c925287a4dc4b 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -495,7 +495,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,

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

if (lock_task_sighand(task, &flags)) {
@@ -529,7 +529,6 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,

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

@@ -542,10 +541,13 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,

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);
}

--
2.43.0

\
 
 \ /
  Last update: 2024-03-13 18:37    [W:0.693 / U:3.252 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site