git.ipfire.org Git - thirdparty/kernel/stable-queue.git/blob

   1 From 60f92acb60a989b14e4b744501a0df0f82ef30a3 Mon Sep 17 00:00:00 2001
   2 From: Oleg Nesterov <oleg@redhat.com>
   3 Date: Tue, 23 Jan 2024 16:33:55 +0100
   4 Subject: fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task_sighand()
   5
   6 From: Oleg Nesterov <oleg@redhat.com>
   7
   8 commit 60f92acb60a989b14e4b744501a0df0f82ef30a3 upstream.
   9
  10 Patch series "fs/proc: do_task_stat: use sig->stats_".
  11
  12 do_task_stat() has the same problem as getrusage() had before "getrusage:
  13 use sig->stats_lock rather than lock_task_sighand()": a hard lockup.  If
  14 NR_CPUS threads call lock_task_sighand() at the same time and the process
  15 has NR_THREADS, spin_lock_irq will spin with irqs disabled O(NR_CPUS *
  16 NR_THREADS) time.
  17
  18
  19 This patch (of 3):
  20
  21 thread_group_cputime() does its own locking, we can safely shift
  22 thread_group_cputime_adjusted() which does another for_each_thread loop
  23 outside of ->siglock protected section.
  24
  25 Not only this removes for_each_thread() from the critical section with
  26 irqs disabled, this removes another case when stats_lock is taken with
  27 siglock held.  We want to remove this dependency, then we can change the
  28 users of stats_lock to not disable irqs.
  29
  30 Link: https://lkml.kernel.org/r/20240123153313.GA21832@redhat.com
  31 Link: https://lkml.kernel.org/r/20240123153355.GA21854@redhat.com
  32 Signed-off-by: Oleg Nesterov <oleg@redhat.com>
  33 Signed-off-by: Dylan Hatch <dylanbhatch@google.com>
  34 Cc: Eric W. Biederman <ebiederm@xmission.com>
  35 Cc: <stable@vger.kernel.org>
  36 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  37 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  38 ---
  39  fs/proc/array.c |   10 ++++++----
  40  1 file changed, 6 insertions(+), 4 deletions(-)
  41
  42 --- a/fs/proc/array.c
  43 +++ b/fs/proc/array.c
  44 @@ -511,7 +511,7 @@ static int do_task_stat(struct seq_file
  45
  46         sigemptyset(&sigign);
  47         sigemptyset(&sigcatch);
  48 -       cutime = cstime = utime = stime = 0;
  49 +       cutime = cstime = 0;
  50         cgtime = gtime = 0;
  51
  52         if (lock_task_sighand(task, &flags)) {
  53 @@ -546,7 +546,6 @@ static int do_task_stat(struct seq_file
  54
  55                         min_flt += sig->min_flt;
  56                         maj_flt += sig->maj_flt;
  57 -                       thread_group_cputime_adjusted(task, &utime, &stime);
  58                         gtime += sig->gtime;
  59
  60                         if (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_STOP_STOPPED))
  61 @@ -562,10 +561,13 @@ static int do_task_stat(struct seq_file
  62
  63         if (permitted && (!whole || num_threads < 2))
  64                 wchan = !task_is_running(task);
  65 -       if (!whole) {
  66 +
  67 +       if (whole) {
  68 +               thread_group_cputime_adjusted(task, &utime, &stime);
  69 +       } else {
  70 +               task_cputime_adjusted(task, &utime, &stime);
  71                 min_flt = task->min_flt;
  72                 maj_flt = task->maj_flt;
  73 -               task_cputime_adjusted(task, &utime, &stime);
  74                 gtime = task_gtime(task);
  75         }
  76