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fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task_sighand()

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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>
This commit is contained in:
Oleg Nesterov 2024-01-23 16:33:55 +01:00 committed by Andrew Morton
parent f7ec1cd5cc
commit 60f92acb60
1 changed files with 6 additions and 4 deletions
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10
fs/proc/array.c
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@ -511,7 +511,7 @@ 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)) {
@ -546,7 +546,6 @@ 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;
if (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_STOP_STOPPED))
@ -562,10 +561,13 @@ 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);
}