From: Thomas Gleixner <tglx@linutronix.de>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>
Cc: oe-lkp@lists.linux.dev, lkp@intel.com,
kernel test robot <oliver.sang@intel.com>
Subject: Re: [bigeasy-staging:futex_local_v6] [futex] 865221325b: WARNING:at_lib/rcuref.c:#rcuref_put_slowpath
Date: Fri, 17 Jan 2025 09:49:35 +0100 [thread overview]
Message-ID: <87r051akps.ffs@tglx> (raw)
In-Reply-To: <20250116233137.v8s-FDdH@linutronix.de>
On Fri, Jan 17 2025 at 00:31, Sebastian Andrzej Siewior wrote:
> On 2024-12-31 16:41:41 [+0800], kernel test robot wrote:
>> [ 184.841511][T52159] rcuref - imbalanced put()
>> [ 184.841536][T52159] WARNING: CPU: 64 PID: 52159 at lib/rcuref.c:267 rcuref_put_slowpath+0x66/0x70
>
> after hours of yelling and cursing:
>
> ref = 0 (via rcuref_init(ref, 1))
> T1 T2
> rcuref_put(ref)
> -> atomic_add_negative_release(-1, ref) # ref -> 0xffffffff
> -> rcuref_put_slowpath(ref)
> rcuref_get(ref)
> -> atomic_add_negative_relaxed(1, &ref->refcnt)
> -> return true; # ref -> 0
>
> rcuref_put(ref)
> -> atomic_add_negative_release(-1, ref) # ref -> 0xffffffff
> -> rcuref_put_slowpath()
>
> -> cnt = atomic_read(&ref->refcnt); # cnt -> 0xffffffff / RCUREF_NOREF
> -> atomic_try_cmpxchg_release(&ref->refcnt, &cnt, RCUREF_DEAD)) # ref -> 0xe0000000 / RCUREF_DEAD
> -> return true
> -> cnt = atomic_read(&ref->refcnt); # cnt -> 0xe0000000 / RCUREF_DEAD
> -> if (cnt > RCUREF_RELEASED) # 0xe0000000 > 0xc0000000
> -> WARN_ONCE(cnt >= RCUREF_RELEASED, "rcuref - imbalanced put()")
Duh. Indeed.
That's a nasty one. Let me think about it.
next prev parent reply other threads:[~2025-01-17 8:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-12-31 8:41 [bigeasy-staging:futex_local_v6] [futex] 865221325b: WARNING:at_lib/rcuref.c:#rcuref_put_slowpath kernel test robot
2025-01-16 23:31 ` Sebastian Andrzej Siewior
2025-01-17 8:49 ` Thomas Gleixner [this message]
2025-01-17 10:03 ` Thomas Gleixner
2025-01-20 17:08 ` Sebastian Andrzej Siewior
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