Messages in this thread | | | Subject | Re: net/atm: warning in alloc_tx/__might_sleep | From | Chas Williams <> | Date | Thu, 12 Jan 2017 05:40:54 -0500 |
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On Wed, 2017-01-11 at 20:36 -0800, Cong Wang wrote: > On Wed, Jan 11, 2017 at 11:46 AM, Michal Hocko <mhocko@kernel.org> wrote: > > On Wed 11-01-17 20:45:25, Michal Hocko wrote: > >> On Wed 11-01-17 09:37:06, Chas Williams wrote: > >> > 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); > >> > >> Blee, this code is just horrendous. But the "fix" is obviously broken! > >> schedule() is just a noop if you do not change the task state and what > >> you are just asking for is a never failing non sleeping allocation - aka > >> a busy loop in the kernel! > > > > And btw. this while loop should be really turned into GFP_KERNEL | > > __GFP_NOFAIL with and explanation why this allocation cannot possibly > > fail. > > I think a nested loop is quite unnecessary, probably due to the code itself > is pretty old. The alloc_tx() is in the outer loop, the alloc_skb() is > in the inner > loop, both seem to wait for a successful GFP allocation. The inner one > is even more unnecessary. > > Of course, I am not surprised MM may already have a mechanism to do > the similar logic. > > There maybe some reason ATM needs such a logic, although other proto > could handle skb allocation failure quite well in ->sendmsg().
I can't think of any particular reason that it needs this loop here. I suspect that the loop for alloc_tx() predates the wait logic in ->sendmsg() and that the original looping was in alloc_tx() initially and was simply never removed. Changes here would date back to before the git conversion.
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