fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task_sighand()
commit 60f92acb60
upstream.
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -511,7 +511,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
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sigemptyset(&sigign);
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sigemptyset(&sigcatch);
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cutime = cstime = utime = stime = 0;
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cutime = cstime = 0;
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cgtime = gtime = 0;
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if (lock_task_sighand(task, &flags)) {
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@ -545,7 +545,6 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
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min_flt += sig->min_flt;
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maj_flt += sig->maj_flt;
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thread_group_cputime_adjusted(task, &utime, &stime);
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gtime += sig->gtime;
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if (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_STOP_STOPPED))
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@ -561,10 +560,13 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
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if (permitted && (!whole || num_threads < 2))
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wchan = !task_is_running(task);
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if (!whole) {
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if (whole) {
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thread_group_cputime_adjusted(task, &utime, &stime);
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} else {
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task_cputime_adjusted(task, &utime, &stime);
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min_flt = task->min_flt;
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maj_flt = task->maj_flt;
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task_cputime_adjusted(task, &utime, &stime);
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gtime = task_gtime(task);
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}
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