: Handle disabled preemption in gfp_any()

[NET]: Handle disabled preemption in gfp_any()

ctnetlink uses netlink_unicast from an atomic_notifier_chain (which is called within a RCU read side critical section) without holding further locks. netlink_unicast calls netlink_trim with the result of gfp_any() for the gfp flags, which are passed down to pskb_expand_header. gfp_any() only checks for softirq context and returns GFP_KERNEL, resulting in this warning:

BUG: sleeping function called from invalid context at mm/slab.c:3032

in_atomic():1, irqs_disabled():0
no locks held by rmmod/7010.

Call Trace:
 [<ffffffff8109467f>] debug_show_held_locks+0x9/0xb
 [<ffffffff8100b0b4>] __might_sleep+0xd9/0xdb
 [<ffffffff810b5082>] __kmalloc+0x68/0x110
 [<ffffffff811ba8f2>] pskb_expand_head+0x4d/0x13b
 [<ffffffff81053147>] netlink_broadcast+0xa5/0x2e0
 [<ffffffff881cd1d7>] :nfnetlink:nfnetlink_send+0x83/0x8a
 [<ffffffff8834f6a6>] :nf_conntrack_netlink:ctnetlink_conntrack_event+0x94c/0x96a
 [<ffffffff810624d6>] notifier_call_chain+0x29/0x3e
 [<ffffffff8106251d>] atomic_notifier_call_chain+0x32/0x60
 [<ffffffff881d266d>] :nf_conntrack:destroy_conntrack+0xa5/0x1d3
 [<ffffffff881d194e>] :nf_conntrack:nf_ct_cleanup+0x8c/0x12c
 [<ffffffff881d4614>] :nf_conntrack:kill_l3proto+0x0/0x13
 [<ffffffff881d482a>] :nf_conntrack:nf_conntrack_l3proto_unregister+0x90/0x94
 [<ffffffff883551b3>] :nf_conntrack_ipv4:nf_conntrack_l3proto_ipv4_fini+0x2b/0x5d
 [<ffffffff8109d44f>] sys_delete_module+0x1b5/0x1e6
 [<ffffffff8105f245>] trace_hardirqs_on_thunk+0x35/0x37
 [<ffffffff8105911e>] system_call+0x7e/0x83

Since netlink_unicast is supposed to be callable from within RCU read side critical sections, make gfp_any() check for in_atomic() instead of in_softirq().

Additionally nfnetlink_send needs to use gfp_any() as well for the call to netlink_broadcast).

---
commit 8ab095fd967d4a0443d869b69325cf97ebad5397
tree 2952a1f3afecb0d8b2f745cdbd42aadbaafe3948
parent 511b0c36b2df2df67ec0a95564999964bc81c494
author Patrick McHardy <[email protected]> Tue, 27 Feb 2007 18:47:29 +0100 committer Patrick McHardy <[email protected]> Tue, 27 Feb 2007 18:47:29 +0100

 include/net/sock.h        |    2 +-
 net/netfilter/nfnetlink.c |    3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

index 03684e7..2c7d60c 100644
@@ -1278,7 +1278,7 @@ static inline int sock_writeable(const s
 
 static inline gfp_t gfp_any(void)
 {
-	return in_softirq() ? GFP_ATOMIC : GFP_KERNEL;
+	return in_atomic() ? GFP_ATOMIC : GFP_KERNEL;
 }
 
 static inline long sock_rcvtimeo(const struct sock *sk, int noblock)

index 1febe2e..22d8e1a 100644
@@ -181,13 +181,12 @@ EXPORT_SYMBOL_GPL(nfnetlink_has_listener
 
 int nfnetlink_send(struct sk_buff *skb, u32 pid, unsigned group, int echo)
 {
-	gfp_t allocation = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;
 	int err = 0;
 
 	NETLINK_CB(skb).dst_group = group;
 	if (echo)
 		atomic_inc(&skb->users);
-	netlink_broadcast(nfnl, skb, pid, group, allocation);
+	netlink_broadcast(nfnl, skb, pid, group, gfp_any());
 	if (echo)
 		err = netlink_unicast(nfnl, skb, pid, MSG_DONTWAIT);
 

From: Patrick McHardy <[email protected]>
Date: Tue, 27 Feb 2007 18:48:19 +0100

Applied, good catch Patrick.

Breaks -rt, but I will submit a patch to Ingo to that will make this fix work in the -rt context. I nevertheless agree that this is a good catch!!!

Thanx, Paul