FAILED: patch "[PATCH] getrusage: use sig->stats_lock rather than" failed to apply to 6.1-stable tree

gregkh
2024-02-19T18:11:51Z

The patch below does not apply to the 6.1-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-6.1.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 '2024021934-version-stamp-e8f4@gregkh' --subject-prefix 'PATCH 6.1.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")

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;