Re: [alsa-devel] usb/sound/usx2y: warning in usb_stream_new/__alloc_pages_slowpath

[Takashi Iwai]

On Thu, 21 Sep 2017 17:38:53 +0200,
Andrey Konovalov wrote:
> 
> Hi!
> 
> I've got the following report while fuzzing the kernel with syzkaller.
> 
> On commit ebb2c2437d8008d46796902ff390653822af6cc4 (Sep 18).
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 1846 at mm/page_alloc.c:3883
> __alloc_pages_slowpath+0x1ef2/0x2d70
> Modules linked in:
> CPU: 1 PID: 1846 Comm: kworker/1:2 Not tainted
> 4.14.0-rc1-42251-gebb2c2437d80 #215
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Workqueue: usb_hub_wq hub_event
> task: ffff8800643c18c0 task.stack: ffff88006b658000
> RIP: 0010:trace_reclaim_retry_zone ./include/trace/events/oom.h:31
> RIP: 0010:should_reclaim_retry mm/page_alloc.c:3783
> RIP: 0010:__alloc_pages_slowpath+0x1ef2/0x2d70 mm/page_alloc.c:4039
> RSP: 0018:ffff88006b65d938 EFLAGS: 00010246
> RAX: 00000000ffffa666 RBX: 00000000014000c0 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000034 RDI: 000000000140c0c0
> RBP: ffff88006b65e088 R08: 0000000000000000 R09: fffffffffff00f88
> R10: 0000000000000000 R11: 0000000000000085 R12: ffff88006b65e130
> R13: ffff88006b65e270 R14: ffff88006b65e0f0 R15: 000000000140c0c0
> FS:  0000000000000000(0000) GS:ffff88006c900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020829000 CR3: 0000000063cce000 CR4: 00000000000006e0
> Call Trace:
>  __alloc_pages_nodemask+0x921/0xf70 mm/page_alloc.c:4217
>  alloc_pages_current+0xbb/0x1f0 mm/mempolicy.c:2035
>  alloc_pages ./include/linux/gfp.h:505
>  __get_free_pages+0x14/0x50 mm/page_alloc.c:4248
>  usb_stream_new+0x50f/0x9f0 sound/usb/usx2y/usb_stream.c:214

The warning itself should be harmless, indicating only that the driver
tries to allocate too high-order memory pages.  The error path handles
the allocation error gracefully, so basically we can suppress the
warning by adding __GFP_NOWARN, in addition to a sanity check in the
caller side.

I've been traveling and will be traveling again in the next week, so
I'll cook up once after back to work again.


thanks,

Takashi