On 6/16/24 10:05, syzbot wrote:
syzbot has bisected this issue to:
commit 21c38a3bd4ee3fb7337d013a638302fb5e5f9dc2
Author: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
Date: Wed May 1 14:04:11 2024 +0000
cgroup/rstat: add cgroup_rstat_cpu_lock helpers and tracepoints
bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16695261980000
start commit: 36534d3c5453 tcp: use signed arithmetic in tcp_rtx_probe0_..
git tree: bpf
final oops: https://syzkaller.appspot.com/x/report.txt?x=15695261980000
console output: https://syzkaller.appspot.com/x/log.txt?x=11695261980000
kernel config: https://syzkaller.appspot.com/x/.config?x=333ebe38d43c42e2
dashboard link: https://syzkaller.appspot.com/bug?extid=6ff90931779bcdfc840c
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1585acfa980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17bdb7ee980000
Reported-by: syzbot+6ff90931779bcdfc840c@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 21c38a3bd4ee ("cgroup/rstat: add cgroup_rstat_cpu_lock helpers and tracepoints")
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
+static __always_inline
+unsigned long _cgroup_rstat_cpu_lock(raw_spinlock_t *cpu_lock, int cpu,
+ struct cgroup *cgrp, const bool
fast_path)
+{
+ unsigned long flags;
+ bool contended;
+
+ /*
+ * The _irqsave() is needed because cgroup_rstat_lock is
+ * spinlock_t which is a sleeping lock on PREEMPT_RT. Acquiring
+ * this lock with the _irq() suffix only disables interrupts on
+ * a non-PREEMPT_RT kernel. The raw_spinlock_t below disables
+ * interrupts on both configurations. The _irqsave() ensures
+ * that interrupts are always disabled and later restored.
+ */
+ contended = !raw_spin_trylock_irqsave(cpu_lock, flags);
+ if (contended) {
+ if (fast_path)
+ trace_cgroup_rstat_cpu_lock_contended_fastpath(cgrp, cp>
+ else
+ trace_cgroup_rstat_cpu_lock_contended(cgrp, cpu,
conten>
+
+ raw_spin_lock_irqsave(cpu_lock, flags);
+ }
I believe the problem may be caused by the fact that
trace_cgroup_rstat_cpu_lock_contended*() can be called with IRQ enabled.
I had suggested before IRQ should be disabled first before doing any
trace operation. See
https://lore.kernel.org/linux-mm/203fdb35-f4cf-4754-9709-3c024eecade9@xxxxxxxxxx/
Doing so may be able to resolve this possible deadlock.
Cheers,
Longman
