linux-kernel - [33/44] net: Fix the condition passed to sk_wait

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Message-Id: <20101208000642.874563691@clark.site>
Date:	Tue, 07 Dec 2010 16:04:32 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Nagendra Singh Tomar <tomer_iisc@...oo.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [33/44] net: Fix the condition passed to sk_wait_event()

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Nagendra Tomar <tomer_iisc@...oo.com>

[ Upstream commit 482964e56e1320cb7952faa1932d8ecf59c4bf75 ]

This patch fixes the condition (3rd arg) passed to sk_wait_event() in
sk_stream_wait_memory(). The incorrect check in sk_stream_wait_memory()
causes the following soft lockup in tcp_sendmsg() when the global tcp
memory pool has exhausted.

>>> snip <<<

localhost kernel: BUG: soft lockup - CPU#3 stuck for 11s! [sshd:6429]
localhost kernel: CPU 3:
localhost kernel: RIP: 0010:[sk_stream_wait_memory+0xcd/0x200]  [sk_stream_wait_memory+0xcd/0x200] sk_stream_wait_memory+0xcd/0x200
localhost kernel:
localhost kernel: Call Trace:
localhost kernel:  [sk_stream_wait_memory+0x1b1/0x200] sk_stream_wait_memory+0x1b1/0x200
localhost kernel:  [<ffffffff802557c0>] autoremove_wake_function+0x0/0x40
localhost kernel:  [ipv6:tcp_sendmsg+0x6e6/0xe90] tcp_sendmsg+0x6e6/0xce0
localhost kernel:  [sock_aio_write+0x126/0x140] sock_aio_write+0x126/0x140
localhost kernel:  [xfs:do_sync_write+0xf1/0x130] do_sync_write+0xf1/0x130
localhost kernel:  [<ffffffff802557c0>] autoremove_wake_function+0x0/0x40
localhost kernel:  [hrtimer_start+0xe3/0x170] hrtimer_start+0xe3/0x170
localhost kernel:  [vfs_write+0x185/0x190] vfs_write+0x185/0x190
localhost kernel:  [sys_write+0x50/0x90] sys_write+0x50/0x90
localhost kernel:  [system_call+0x7e/0x83] system_call+0x7e/0x83

>>> snip <<<

What is happening is, that the sk_wait_event() condition passed from
sk_stream_wait_memory() evaluates to true for the case of tcp global memory
exhaustion. This is because both sk_stream_memory_free() and vm_wait are true
which causes sk_wait_event() to *not* call schedule_timeout().
Hence sk_stream_wait_memory() returns immediately to the caller w/o sleeping.
This causes the caller to again try allocation, which again fails and again
calls sk_stream_wait_memory(), and so on.

[ Bug introduced by commit c1cbe4b7ad0bc4b1d98ea708a3fecb7362aa4088
  ("[NET]: Avoid atomic xchg() for non-error case") -DaveM ]

Signed-off-by: Nagendra Singh Tomar <tomer_iisc@...oo.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 net/core/stream.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/core/stream.c
+++ b/net/core/stream.c
@@ -139,10 +139,10 @@ int sk_stream_wait_memory(struct sock *s

 		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
 		sk->sk_write_pending++;
-		sk_wait_event(sk, &current_timeo, !sk->sk_err &&
-						  !(sk->sk_shutdown & SEND_SHUTDOWN) &&
-						  sk_stream_memory_free(sk) &&
-						  vm_wait);
+		sk_wait_event(sk, &current_timeo, sk->sk_err ||
+						  (sk->sk_shutdown & SEND_SHUTDOWN) ||
+						  (sk_stream_memory_free(sk) &&
+						  !vm_wait));
 		sk->sk_write_pending--;

 		if (vm_wait) {

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