Subject: Re: net/atm: warning in alloc_tx/__might_sleep

From: Chas Williams <[email-masked]>
Date: Wed, 11 Jan 2017 09:37:06 -0500

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);