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Message-ID: <CAAeHK+z=KB8+Gy43BpFVG+bbfsQzvX59KFbftvipPefghsUKcQ@mail.gmail.com> Date: Mon, 13 Mar 2017 18:43:51 +0100 From: Andrey Konovalov <andreyknvl@...gle.com> To: Chas Williams <3chas3@...il.com> Cc: Cong Wang <xiyou.wangcong@...il.com>, Michal Hocko <mhocko@...nel.org>, "David S. Miller" <davem@...emloft.net>, Alexey Kuznetsov <kuznet@....inr.ac.ru>, 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>, 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 Thu, Jan 12, 2017 at 11:40 AM, Chas Williams <3chas3@...il.com> wrote: > On Wed, 2017-01-11 at 20:36 -0800, Cong Wang wrote: >> On Wed, Jan 11, 2017 at 11:46 AM, Michal Hocko <mhocko@...nel.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. > Hi, I'm still seeing this on 4495c08e84729385774601b5146d51d9e5849f81 (4.11-rc2). Thanks!
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