linux-kernel - Re: net/atm: warning in alloc_tx/__might

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Date:   Wed, 11 Jan 2017 09:37:06 -0500
From:   Chas Williams <3chas3@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/atm: warning in alloc_tx/__might_sleep

On Mon, 2017-01-09 at 18:20 +0100, Andrey Konovalov wrote:
> Hi!
> 
> I've got the following error report while running the syzkaller fuzzer.
> 
> On commit a121103c922847ba5010819a3f250f1f7fc84ab8 (4.10-rc3).
> 
> A reproducer is attached.
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 4114 at kernel/sched/core.c:7737 __might_sleep+0x149/0x1a0
> do not call blocking ops when !TASK_RUNNING; state=1 set at
> [<ffffffff813fcb22>] prepare_to_wait+0x182/0x530
> Modules linked in:
> CPU: 0 PID: 4114 Comm: a.out Not tainted 4.10.0-rc3+ #59
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:15
>  dump_stack+0x292/0x398 lib/dump_stack.c:51
>  __warn+0x19f/0x1e0 kernel/panic.c:547
>  warn_slowpath_fmt+0xc5/0x110 kernel/panic.c:562
>  __might_sleep+0x149/0x1a0 kernel/sched/core.c:7732
>  slab_pre_alloc_hook mm/slab.h:408
>  slab_alloc_node mm/slub.c:2634
>  kmem_cache_alloc_node+0x14a/0x280 mm/slub.c:2744
>  __alloc_skb+0x10f/0x800 net/core/skbuff.c:219
>  alloc_skb ./include/linux/skbuff.h:926
>  alloc_tx net/atm/common.c:75

This is likely alloc_skb(..., GFP_KERNEL) in alloc_tx().  The simplest
fix for this would be simply to switch this GFP_ATOMIC.  See if this is
any better.

diff --git a/net/atm/common.c b/net/atm/common.c
index a3ca922..d84220c 100644
--- a/net/atm/common.c
+++ b/net/atm/common.c
@@ -72,7 +72,7 @@ static struct sk_buff *alloc_tx(struct atm_vcc *vcc, unsigned int size)
 			 sk_wmem_alloc_get(sk), size, sk->sk_sndbuf);
 		return NULL;
 	}
-	while (!(skb = alloc_skb(size, GFP_KERNEL)))
+	while (!(skb = alloc_skb(size, GFP_ATOMIC)))
 		schedule();
 	pr_debug("%d += %d\n", sk_wmem_alloc_get(sk), skb->truesize);
 	atomic_add(skb->truesize, &sk->sk_wmem_alloc);