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Sat, 30 Aug 2025 14:56:48 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com Authentication-Results: sina.com; spf=none smtp.mailfrom=hdanton@sina.com; dkim=none header.i=none; dmarc=none action=none header.from=hdanton@sina.com X-SMAIL-MID: 7084846685059 X-SMAIL-UIID: A6FAEFE71B924319A6F4B3787D874418-20250830-145648-1 From: Hillf Danton To: syzbot Cc: Sebastian Andrzej Siewior , linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [sound?] possible deadlock in __snd_pcm_lib_xfer (2) Date: Sat, 30 Aug 2025 14:56:37 +0800 Message-ID: <20250830065638.6116-1-hdanton@sina.com> In-Reply-To: <68b269e9.a00a0220.1337b0.001f.GAE@google.com> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit > Date: Fri, 29 Aug 2025 20:03:05 -0700 > Hello, > > syzbot has tested the proposed patch but the reproducer is still triggering an issue: > possible deadlock in __snd_pcm_lib_xfer > > ====================================================== > WARNING: possible circular locking dependency detected > syzkaller #0 Not tainted > ------------------------------------------------------ > syz.0.46/6843 is trying to acquire lock: > ffff8880b8823d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline] > ffff8880b8823d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: __local_bh_disable_ip+0x264/0x400 kernel/softirq.c:168 > Given softirq_ctrl is percpu, this report is false positive. > but task is already holding lock: > ffff88814ccb7150 (&group->lock#2){+.+.}-{3:3}, at: __snd_pcm_lib_xfer+0x386/0x1ce0 sound/core/pcm_lib.c:2319 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #1 (&group->lock#2){+.+.}-{3:3}: > lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 > rt_spin_lock+0x88/0x2c0 kernel/locking/spinlock_rt.c:56 > spin_lock include/linux/spinlock_rt.h:44 [inline] > _snd_pcm_stream_lock_irqsave+0x7c/0xa0 sound/core/pcm_native.c:171 > class_pcm_stream_lock_irqsave_constructor include/sound/pcm.h:682 [inline] > snd_pcm_period_elapsed+0x1e/0x80 sound/core/pcm_lib.c:1938 > dummy_hrtimer_callback+0x80/0x180 sound/drivers/dummy.c:386 > __run_hrtimer kernel/time/hrtimer.c:1763 [inline] > __hrtimer_run_queues+0x590/0xda0 kernel/time/hrtimer.c:1829 > hrtimer_run_softirq+0x1a3/0x2e0 kernel/time/hrtimer.c:1847 > handle_softirqs+0x22c/0x710 kernel/softirq.c:579 > __do_softirq kernel/softirq.c:613 [inline] > run_ktimerd+0xcf/0x190 kernel/softirq.c:1043 > smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160 > kthread+0x711/0x8a0 kernel/kthread.c:463 > ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 > > -> #0 ((softirq_ctrl.lock)){+.+.}-{3:3}: > check_prev_add kernel/locking/lockdep.c:3165 [inline] > check_prevs_add kernel/locking/lockdep.c:3284 [inline] > validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908 > __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 > reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385 > __lock_release kernel/locking/lockdep.c:5574 [inline] > lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889 > __local_bh_enable_ip+0x10c/0x270 kernel/softirq.c:228 > hrtimer_cancel+0x39/0x60 kernel/time/hrtimer.c:1491 > dummy_hrtimer_stop+0xcf/0x100 sound/drivers/dummy.c:410 > snd_pcm_do_stop+0x12a/0x1c0 sound/core/pcm_native.c:1525 > snd_pcm_action_single sound/core/pcm_native.c:1305 [inline] > snd_pcm_action+0xe4/0x240 sound/core/pcm_native.c:1388 > __snd_pcm_xrun+0x27f/0x7c0 sound/core/pcm_lib.c:180 > snd_pcm_update_state+0x342/0x430 sound/core/pcm_lib.c:224 > snd_pcm_update_hw_ptr0+0x10b2/0x1b00 sound/core/pcm_lib.c:493 > snd_pcm_update_hw_ptr sound/core/pcm_lib.c:499 [inline] > __snd_pcm_lib_xfer+0x510/0x1ce0 sound/core/pcm_lib.c:2326 > snd_pcm_oss_write3+0x1bc/0x320 sound/core/oss/pcm_oss.c:1241 > snd_pcm_plug_write_transfer+0x2cb/0x4c0 sound/core/oss/pcm_plugin.c:630 > snd_pcm_oss_write2 sound/core/oss/pcm_oss.c:1373 [inline] > snd_pcm_oss_write1 sound/core/oss/pcm_oss.c:1439 [inline] > snd_pcm_oss_write+0xba2/0x11a0 sound/core/oss/pcm_oss.c:2795 > vfs_write+0x287/0xb40 fs/read_write.c:684 > ksys_write+0x14b/0x260 fs/read_write.c:738 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&group->lock#2); > lock((softirq_ctrl.lock)); > lock(&group->lock#2); > lock((softirq_ctrl.lock)); > > *** DEADLOCK *** > > 2 locks held by syz.0.46/6843: > #0: ffff88814ccb7150 (&group->lock#2){+.+.}-{3:3}, at: __snd_pcm_lib_xfer+0x386/0x1ce0 sound/core/pcm_lib.c:2319 > #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline] > #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline] > #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline] > #1: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1bb/0x2c0 kernel/locking/spinlock_rt.c:57 > > stack backtrace: > CPU: 0 UID: 0 PID: 6843 Comm: syz.0.46 Not tainted syzkaller #0 PREEMPT_{RT,(full)} > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 > Call Trace: > > dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 > print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043 > check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175 > check_prev_add kernel/locking/lockdep.c:3165 [inline] > check_prevs_add kernel/locking/lockdep.c:3284 [inline] > validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908 > __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 > reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385 > __lock_release kernel/locking/lockdep.c:5574 [inline] > lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889 > __local_bh_enable_ip+0x10c/0x270 kernel/softirq.c:228 > hrtimer_cancel+0x39/0x60 kernel/time/hrtimer.c:1491 > dummy_hrtimer_stop+0xcf/0x100 sound/drivers/dummy.c:410 > snd_pcm_do_stop+0x12a/0x1c0 sound/core/pcm_native.c:1525 > snd_pcm_action_single sound/core/pcm_native.c:1305 [inline] > snd_pcm_action+0xe4/0x240 sound/core/pcm_native.c:1388 > __snd_pcm_xrun+0x27f/0x7c0 sound/core/pcm_lib.c:180 > snd_pcm_update_state+0x342/0x430 sound/core/pcm_lib.c:224 > snd_pcm_update_hw_ptr0+0x10b2/0x1b00 sound/core/pcm_lib.c:493 > snd_pcm_update_hw_ptr sound/core/pcm_lib.c:499 [inline] > __snd_pcm_lib_xfer+0x510/0x1ce0 sound/core/pcm_lib.c:2326 > snd_pcm_oss_write3+0x1bc/0x320 sound/core/oss/pcm_oss.c:1241 > snd_pcm_plug_write_transfer+0x2cb/0x4c0 sound/core/oss/pcm_plugin.c:630 > snd_pcm_oss_write2 sound/core/oss/pcm_oss.c:1373 [inline] > snd_pcm_oss_write1 sound/core/oss/pcm_oss.c:1439 [inline] > snd_pcm_oss_write+0xba2/0x11a0 sound/core/oss/pcm_oss.c:2795 > vfs_write+0x287/0xb40 fs/read_write.c:684 > ksys_write+0x14b/0x260 fs/read_write.c:738 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7f9528fcebe9 > Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007f952863e038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 > RAX: ffffffffffffffda RBX: 00007f95291f5fa0 RCX: 00007f9528fcebe9 > RDX: 000000000000fc36 RSI: 0000200000000500 RDI: 0000000000000003 > RBP: 00007f9529051e19 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > R13: 00007f95291f6038 R14: 00007f95291f5fa0 R15: 00007ffe192e0268 > > > > Tested on: > > commit: 11e7861d Merge tag 'for-linus' of git://git.kernel.org.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=15d8d634580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=bd9738e00c1bbfb4 > dashboard link: https://syzkaller.appspot.com/bug?extid=10b4363fb0f46527f3f3 > compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 > patch: https://syzkaller.appspot.com/x/patch.diff?x=11b7fef0580000 > >