linux-kernel - Re: [alsa-devel] WARNING in snd_pcm_hw_param

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Date:   Mon, 1 Jan 2018 11:29:51 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Takashi Iwai <tiwai@...e.de>,
        syzbot <syzbot+6f11c7e2a1b91d466432@...kaller.appspotmail.com>
Cc:     linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
        syzkaller-bugs@...glegroups.com, mingo@...nel.org
Subject: Re: [alsa-devel] WARNING in snd_pcm_hw_param_first

On 01/01/2018 10:03 AM, Takashi Iwai wrote:
[...]
>> CPU: 0 PID: 3502 Comm: syzkaller781065 Not tainted 4.15.0-rc5+ #154
>> Hardware name: Google Google Compute Engine/Google Compute Engine,
>> BIOS  Google 01/01/2011
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:17 [inline]
>>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>>  panic+0x1e4/0x41c kernel/panic.c:183
>>  __warn+0x1dc/0x200 kernel/panic.c:547
>>  report_bug+0x211/0x2d0 lib/bug.c:184
>>  fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
>>  fixup_bug arch/x86/kernel/traps.c:247 [inline]
>>  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
>>  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
>>  invalid_op+0x22/0x40 arch/x86/entry/entry_64.S:1079
>> RIP: 0010:snd_pcm_hw_param_first+0x289/0x690 sound/core/pcm_lib.c:1635
>> RSP: 0018:ffff8801c013f1a0 EFLAGS: 00010293
>> RAX: ffff8801c03bc3c0 RBX: ffff8801bff08dc0 RCX: ffffffff841bee19
>> RDX: 0000000000000000 RSI: 00000000ffffffea RDI: ffffed0038027e28
>> RBP: ffff8801c013f1f0 R08: ffffed0038027d63 R09: ffff8801c013eb10
>> R10: 0000000000000001 R11: ffffed0038027d62 R12: 000000000000000d
>> R13: 00000000ffffffea R14: 0000000000000005 R15: 0000000000002000
>>  snd_pcm_hw_param_near.constprop.27+0x78d/0x9a0 sound/core/oss/pcm_oss.c:457
>>  snd_pcm_oss_change_params+0x17d3/0x3720 sound/core/oss/pcm_oss.c:969
>>  snd_pcm_oss_make_ready+0xaa/0x130 sound/core/oss/pcm_oss.c:1128
>>  snd_pcm_oss_sync+0x257/0x830 sound/core/oss/pcm_oss.c:1638
>>  snd_pcm_oss_release+0x20b/0x280 sound/core/oss/pcm_oss.c:2431
>>  __fput+0x327/0x7e0 fs/file_table.c:210
>>  ____fput+0x15/0x20 fs/file_table.c:244
>>  task_work_run+0x199/0x270 kernel/task_work.c:113
>>  exit_task_work include/linux/task_work.h:22 [inline]
>>  do_exit+0x9bb/0x1ad0 kernel/exit.c:865
>>  do_group_exit+0x149/0x400 kernel/exit.c:968
>>  SYSC_exit_group kernel/exit.c:979 [inline]
>>  SyS_exit_group+0x1d/0x20 kernel/exit.c:977
>>  do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
>>  do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
>>  entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:129
>> RIP: 0023:0xf7f4ec79
>> RSP: 002b:00000000ffc2c18c EFLAGS: 00000292 ORIG_RAX: 00000000000000fc
>> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000080f0298
>> RDX: 0000000000000000 RSI: 00000000080d9b78 RDI: 00000000080f02a0
>> RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
>> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>> Dumping ftrace buffer:
>>    (ftrace buffer empty)
>> Kernel Offset: disabled
>> Rebooting in 86400 seconds..
> 
> This must be a superfluous WARN_ON() call invoked by snd_BUG_ON()
> check that can be safely ignored.  A quick fix patch is below.

I believe those snd_BUG_ON() are there because these calls to refine
should never fail based on the checks done earlier. And them triggering
indicates that something is wrong somewhere else.