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Subject[34-longterm 194/260] net: Fix the condition passed to sk_wait_event()
Date
From: Nagendra Tomar <tomer_iisc@yahoo.com>

commit 482964e56e1320cb7952faa1932d8ecf59c4bf75 upstream.

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@yahoo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
net/core/stream.c | 8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/net/core/stream.c b/net/core/stream.c
index a37debf..e48c85f 100644
--- a/net/core/stream.c
+++ b/net/core/stream.c
@@ -140,10 +140,10 @@ int sk_stream_wait_memory(struct sock *sk, long *timeo_p)

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) {
--
1.7.3.3


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