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Date: Thu, 15 Oct 2015 07:32:03 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: Nikolay Borisov <kernel@...p.com>
Cc: kadlec@...ckhole.kfki.hu, pablo@...filter.org, davem@...emloft.net,
netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
operations@...eground.com
Subject: Re: [PATCH v2] netfilter: ipset: Fix sleeping memory allocation in
atomic context
On Thu, 2015-10-15 at 16:41 +0300, Nikolay Borisov wrote:
>
> On 10/15/2015 04:32 PM, Eric Dumazet wrote:
> > On Thu, 2015-10-15 at 13:56 +0300, Nikolay Borisov wrote:
> >> Commit 00590fdd5be0 introduced RCU locking in list type and in
> >> doing so introduced a memory allocation in list_set_add, which
> >> results in the following splat:
> >>
> >> BUG: sleeping function called from invalid context at mm/page_alloc.c:2759
> >> in_atomic(): 1, irqs_disabled(): 0, pid: 9664, name: ipset
> >> CPU: 18 PID: 9664 Comm: ipset Tainted: G O 3.12.47-clouder3 #1
> >> Hardware name: Supermicro X10DRi/X10DRi, BIOS 1.1 04/14/2015
> >> 0000000000000002 ffff881fd14273c8 ffffffff8163d891 ffff881fcb4264b0
> >> ffff881fcb4260c0 ffff881fd14273e8 ffffffff810ba5bf ffff881fd1427558
> >> 0000000000000000 ffff881fd1427568 ffffffff81142b33 ffff881f00000000
> >> Call Trace:
> >> [<ffffffff8163d891>] dump_stack+0x58/0x7f
> >> [<ffffffff810ba5bf>] __might_sleep+0xdf/0x110
> >> [<ffffffff81142b33>] __alloc_pages_nodemask+0x243/0xc20
> >> [<ffffffff81181c6e>] alloc_pages_current+0xbe/0x170
> >> [<ffffffff81188315>] new_slab+0x295/0x340
> >> [<ffffffff81189a40>] __slab_alloc+0x2c0/0x5a0
> >> [<ffffffff8164000c>] ? __schedule+0x2dc/0x760
> >> [<ffffffff8118a71b>] __kmalloc+0x11b/0x230
> >> [<ffffffffa02bd0ac>] ? ip_set_get_byname+0xec/0x100 [ip_set]
> >> [<ffffffffa02d23fb>] list_set_uadd+0x16b/0x314 [ip_set_list_set]
> >> [<ffffffff81642148>] ? _raw_write_unlock_bh+0x28/0x30
> >> [<ffffffffa02d1cfc>] list_set_uadt+0x21c/0x320 [ip_set_list_set]
> >> [<ffffffffa02d2290>] ? list_set_create+0x1a0/0x1a0 [ip_set_list_set]
> >> [<ffffffffa02be242>] call_ad+0x82/0x200 [ip_set]
> >> [<ffffffffa02bb171>] ? find_set_type+0x51/0xa0 [ip_set]
> >> [<ffffffff8133f275>] ? nla_parse+0xf5/0x130
> >> [<ffffffffa02be8ae>] ip_set_uadd+0x20e/0x2d0 [ip_set]
> >> [<ffffffffa02be013>] ? ip_set_create+0x2a3/0x450 [ip_set]
> >> [<ffffffffa02be6a0>] ? ip_set_udel+0x2e0/0x2e0 [ip_set]
> >> [<ffffffff815b316e>] nfnetlink_rcv_msg+0x31e/0x330
> >> [<ffffffff815b2e91>] ? nfnetlink_rcv_msg+0x41/0x330
> >> [<ffffffff815b2e50>] ? nfnl_lock+0x30/0x30
> >> [<ffffffff815ae179>] netlink_rcv_skb+0xa9/0xd0
> >> [<ffffffff815b2d45>] nfnetlink_rcv+0x15/0x20
> >> [<ffffffff815ade5f>] netlink_unicast+0x10f/0x190
> >> [<ffffffff815aedb0>] netlink_sendmsg+0x2c0/0x660
> >> [<ffffffff81567f00>] sock_sendmsg+0x90/0xc0
> >> [<ffffffff81565b03>] ? move_addr_to_user+0xa3/0xc0
> >> [<ffffffff81568552>] ? ___sys_recvmsg+0x182/0x300
> >> [<ffffffff81568064>] SYSC_sendto+0x134/0x180
> >> [<ffffffff811c4e01>] ? mntput+0x21/0x30
> >> [<ffffffff81572d2f>] ? __kfree_skb+0x3f/0xa0
> >> [<ffffffff815680be>] SyS_sendto+0xe/0x10
> >> [<ffffffff816434b2>] system_call_fastpath+0x16/0x1b
> >>
> >> The call chain leading to this is as follow:
> >> call_ad -> list_set_uadt -> list_set_uadd -> kzalloc(, GFP_KERNEL).
> >> And since GFP_KERNEL allows initiating direct reclaim thus
> >> potentially sleeping in the allocation path, this leads to the
> >> aforementioned splat.
> >>
> >> To fix it change the allocation type to GFP_ATOMIC, to
> >> correctly reflect that it is occuring in an atomic context.
> >>
> >> Fixes: 00590fdd5be0 ("netfilter: ipset: Introduce RCU locking in list type")
> >>
> >> Acked-by: Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
> >> Signed-off-by: Nikolay Borisov <kernel@...p.com>
> >> ---
> >>
> >> Changes since V1:
> >> * Added acked-by
> >> * Fixed patch header
> >>
> >> net/netfilter/ipset/ip_set_list_set.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/net/netfilter/ipset/ip_set_list_set.c b/net/netfilter/ipset/ip_set_list_set.c
> >> index a1fe537..5a30ce6 100644
> >> --- a/net/netfilter/ipset/ip_set_list_set.c
> >> +++ b/net/netfilter/ipset/ip_set_list_set.c
> >> @@ -297,7 +297,7 @@ list_set_uadd(struct ip_set *set, void *value, const struct ip_set_ext *ext,
> >> ip_set_timeout_expired(ext_timeout(n, set))))
> >> n = NULL;
> >>
> >> - e = kzalloc(set->dsize, GFP_KERNEL);
> >> + e = kzalloc(set->dsize, GFP_ATOMIC);
> >> if (!e)
> >> return -ENOMEM;
> >> e->id = d->id;
> >
> > This patch looks very bogus to me.
> >
> > Could we fix the root cause please ?
> >
> > Root cause is that somewhere in this controlling path, an erroneous
> > rcu_read_lock() is used, while it is very probably not needed, as
> > controlling path should be protected by a mutex, which definitely is
> > sane, because it allows us to perform GFP_KERNEL allocations and being
> > preempted.
> >
> > Why are we using rcu_read_lock() in list_set_list() ?
> >
> > This looks as yet another bit of 'let us throw
> > rcu_read_lock()/rcu_read_unlock() pairs' all over the places because it
> > feels so good.
>
> I did check the call paths and there isn't an rcu_read_lock called in
> list_set_uadt/list_set_uadd. On the contrary, this "write" operation to
> the list is being serialised in call_ad() via set->lock spin_lock.
>
> What am I missing here?
I was not complaining to you, but to Jozsef ;)
Looking at commit 00590fdd5be0d7 terse changelog, we have to look at
whole commit, and find suspicious rcu_read_lock()
Apparently, before this commit, allocations were safe, in process
context (and using GFP_KERNEL), but after the commit, we have the
unfortunate side effect of having potential burst of allocations
done from bh context, using the special reserves dedicated to GFP_ATOMIC
true users (processing packets from softirq handlers)
I hate when we add more GFP_ATOMIC allocations all over the places,
as this increases the risk of depleting memory reserves.
Can the spinlock be converted to a mutex ? If not, then instead of
putting a stack trace in your changelog, a good explanation would be
more useful.
Thanks !
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