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getrusage: use sig->stats_lock rather than lock_task_sighand()

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[ Upstream commit f7ec1cd5cc ]

lock_task_sighand() can trigger a hard lockup. If NR_CPUS threads call
getrusage() at the same time and the process has NR_THREADS, spin_lock_irq
will spin with irqs disabled O(NR_CPUS * NR_THREADS) time.

Change getrusage() to use sig->stats_lock, it was specifically designed
for this type of use. This way it runs lockless in the likely case.

TODO:
	- Change do_task_stat() to use sig->stats_lock too, then we can
	  remove spin_lock_irq(siglock) in wait_task_zombie().

	- Turn sig->stats_lock into seqcount_rwlock_t, this way the
	  readers in the slow mode won't exclude each other. See
	  https://lore.kernel.org/all/20230913154907.GA26210@redhat.com/

	- stats_lock has to disable irqs because ->siglock can be taken
	  in irq context, it would be very nice to change __exit_signal()
	  to avoid the siglock->stats_lock dependency.

Link: https://lkml.kernel.org/r/20240122155053.GA26214@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Dylan Hatch <dylanbhatch@google.com>
Tested-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>
This commit is contained in:
Oleg Nesterov 2024-01-22 16:50:53 +01:00 committed by Sasha Levin
parent 2a304d8c92
commit 9793a3bb53
1 changed files with 13 additions and 3 deletions
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16
kernel/sys.c
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@ -1781,7 +1781,9 @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
unsigned long maxrss;
struct mm_struct *mm;
struct signal_struct *sig = p->signal;
unsigned int seq = 0;
retry:
memset(r, 0, sizeof(*r));
utime = stime = 0;
maxrss = 0;
@ -1793,8 +1795,7 @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
goto out_thread;
}
if (!lock_task_sighand(p, &flags))
return;
flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq);
switch (who) {
case RUSAGE_BOTH:
@ -1822,14 +1823,23 @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
r->ru_oublock += sig->oublock;
if (maxrss < sig->maxrss)
maxrss = sig->maxrss;
rcu_read_lock();
__for_each_thread(sig, t)
accumulate_thread_rusage(t, r);
rcu_read_unlock();
break;
default:
BUG();
}
unlock_task_sighand(p, &flags);
if (need_seqretry(&sig->stats_lock, seq)) {
seq = 1;
goto retry;
}
done_seqretry_irqrestore(&sig->stats_lock, seq, flags);
if (who == RUSAGE_CHILDREN)
goto out_children;