Date:   Mon, 2 Oct 2017 16:34:57 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     alsa-devel@...a-project.org, Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Markus Elfring <elfring@...rs.sourceforge.net>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [alsa-devel] usb/sound/usx2y: warning in usb_stream_new/__alloc_pages_slowpath

On Mon, Oct 2, 2017 at 2:14 PM, Takashi Iwai <tiwai@...e.de> wrote:
> 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.

Hi Takashi,

Your patch fixes the report triggered by my reproducer.

Thanks!

Tested-by: Andrey Konovalov <andreyknvl@...gle.com>

>
>
> thanks,
>
> Takashi
>
> -- 8< --
> From: Takashi Iwai <tiwai@...e.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@...gle.com>
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@...e.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
>
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