The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y git checkout FETCH_HEAD git cherry-pick -x f7ec1cd5cc7ef3ad964b677ba82b8b77f1c93009 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024021941-showman-diaper-6105@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

f7ec1cd5cc7e ("getrusage: use sig->stats_lock rather than lock_task_sighand()") daa694e41375 ("getrusage: move thread_group_cputime_adjusted() outside of lock_task_sighand()") 13b7bc60b535 ("getrusage: use __for_each_thread()") c7ac8231ace9 ("getrusage: add the "signal_struct *sig" local variable") bdd565f817a7 ("y2038: rusage: use __kernel_old_timeval")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f7ec1cd5cc7ef3ad964b677ba82b8b77f1c93009 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov oleg@redhat.com Date: Mon, 22 Jan 2024 16:50:53 +0100 Subject: [PATCH] getrusage: use sig->stats_lock rather than lock_task_sighand()

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

diff --git a/kernel/sys.c b/kernel/sys.c index 70ad06ad852e..f8e543f1e38a 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1788,7 +1788,9 @@ 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; @@ -1800,8 +1802,7 @@ 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: @@ -1829,14 +1830,23 @@ 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;