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

[Takashi Iwai <tiwai@suse.de>]

On Fri, 22 Sep 2017 11:35:49 +0200,
Takashi Iwai wrote:
> 
> 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.

Andrey, could you check the patch below?  It should suppress the
spurious warnings.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: usx2y: Suppress kernel warning at page allocation
 failures

The usx2y driver allocates the stream read/write buffers in continuous
pages depending on the stream setup, and this may spew the kernel
warning messages with a stack trace like:
  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
  ....

It may confuse user as if it were any serious error, although this is
no fatal error and the driver handles the error case gracefully.
Since the driver has already some sanity check of the given size (128
and 256 pages), it can't pass any crazy value.  So it's merely page
fragmentation.

This patch adds __GFP_NOWARN to each caller for suppressing such
kernel warnings.  The original issue was spotted by syzkaller.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/usb/usx2y/usb_stream.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/sound/usb/usx2y/usb_stream.c b/sound/usb/usx2y/usb_stream.c
index 4dab49080700..e229abd21652 100644
--- a/sound/usb/usx2y/usb_stream.c
+++ b/sound/usb/usx2y/usb_stream.c
@@ -191,7 +191,8 @@ struct usb_stream *usb_stream_new(struct usb_stream_kernel *sk,
 	}
 
 	pg = get_order(read_size);
-	sk->s = (void *) __get_free_pages(GFP_KERNEL|__GFP_COMP|__GFP_ZERO, pg);
+	sk->s = (void *) __get_free_pages(GFP_KERNEL|__GFP_COMP|__GFP_ZERO|
+					  __GFP_NOWARN, pg);
 	if (!sk->s) {
 		snd_printk(KERN_WARNING "couldn't __get_free_pages()\n");
 		goto out;
@@ -211,7 +212,8 @@ struct usb_stream *usb_stream_new(struct usb_stream_kernel *sk,
 	pg = get_order(write_size);
 
 	sk->write_page =
-		(void *)__get_free_pages(GFP_KERNEL|__GFP_COMP|__GFP_ZERO, pg);
+		(void *)__get_free_pages(GFP_KERNEL|__GFP_COMP|__GFP_ZERO|
+					 __GFP_NOWARN, pg);
 	if (!sk->write_page) {
 		snd_printk(KERN_WARNING "couldn't __get_free_pages()\n");
 		usb_stream_free(sk);
-- 
2.14.1