From 144d56e91044181ec0ef67aeca91e9a8b5718348 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 20 Aug 2012 00:22:46 +0000 Subject: tcp: fix possible socket refcount problem Commit 6f458dfb40 (tcp: improve latencies of timer triggered events) added bug leading to following trace : [ 2866.131281] IPv4: Attempt to release TCP socket in state 1 ffff880019ec0000 [ 2866.131726] [ 2866.132188] ========================= [ 2866.132281] [ BUG: held lock freed! ] [ 2866.132281] 3.6.0-rc1+ #622 Not tainted [ 2866.132281] ------------------------- [ 2866.132281] kworker/0:1/652 is freeing memory ffff880019ec0000-ffff880019ec0a1f, with a lock still held there! [ 2866.132281] (sk_lock-AF_INET-RPC){+.+...}, at: [] tcp_sendmsg+0x29/0xcc6 [ 2866.132281] 4 locks held by kworker/0:1/652: [ 2866.132281] #0: (rpciod){.+.+.+}, at: [] process_one_work+0x1de/0x47f [ 2866.132281] #1: ((&task->u.tk_work)){+.+.+.}, at: [] process_one_work+0x1de/0x47f [ 2866.132281] #2: (sk_lock-AF_INET-RPC){+.+...}, at: [] tcp_sendmsg+0x29/0xcc6 [ 2866.132281] #3: (&icsk->icsk_retransmit_timer){+.-...}, at: [] run_timer_softirq+0x1ad/0x35f [ 2866.132281] [ 2866.132281] stack backtrace: [ 2866.132281] Pid: 652, comm: kworker/0:1 Not tainted 3.6.0-rc1+ #622 [ 2866.132281] Call Trace: [ 2866.132281] [] debug_check_no_locks_freed+0x112/0x159 [ 2866.132281] [] ? __sk_free+0xfd/0x114 [ 2866.132281] [] kmem_cache_free+0x6b/0x13a [ 2866.132281] [] __sk_free+0xfd/0x114 [ 2866.132281] [] sk_free+0x1c/0x1e [ 2866.132281] [] tcp_write_timer+0x51/0x56 [ 2866.132281] [] run_timer_softirq+0x218/0x35f [ 2866.132281] [] ? run_timer_softirq+0x1ad/0x35f [ 2866.132281] [] ? rb_commit+0x58/0x85 [ 2866.132281] [] ? tcp_write_timer_handler+0x148/0x148 [ 2866.132281] [] __do_softirq+0xcb/0x1f9 [ 2866.132281] [] ? _raw_spin_unlock+0x29/0x2e [ 2866.132281] [] call_softirq+0x1c/0x30 [ 2866.132281] [] do_softirq+0x4a/0xa6 [ 2866.132281] [] irq_exit+0x51/0xad [ 2866.132281] [] do_IRQ+0x9d/0xb4 [ 2866.132281] [] common_interrupt+0x6f/0x6f [ 2866.132281] [] ? sched_clock_cpu+0x58/0xd1 [ 2866.132281] [] ? _raw_spin_unlock_irqrestore+0x4c/0x56 [ 2866.132281] [] mod_timer+0x178/0x1a9 [ 2866.132281] [] sk_reset_timer+0x19/0x26 [ 2866.132281] [] tcp_rearm_rto+0x99/0xa4 [ 2866.132281] [] tcp_event_new_data_sent+0x6e/0x70 [ 2866.132281] [] tcp_write_xmit+0x7de/0x8e4 [ 2866.132281] [] ? __alloc_skb+0xa0/0x1a1 [ 2866.132281] [] __tcp_push_pending_frames+0x2e/0x8a [ 2866.132281] [] tcp_sendmsg+0xb32/0xcc6 [ 2866.132281] [] inet_sendmsg+0xaa/0xd5 [ 2866.132281] [] ? inet_autobind+0x5f/0x5f [ 2866.132281] [] ? trace_clock_local+0x9/0xb [ 2866.132281] [] sock_sendmsg+0xa3/0xc4 [ 2866.132281] [] ? rb_reserve_next_event+0x26f/0x2d5 [ 2866.132281] [] ? native_sched_clock+0x29/0x6f [ 2866.132281] [] ? sched_clock+0x9/0xd [ 2866.132281] [] ? trace_clock_local+0x9/0xb [ 2866.132281] [] kernel_sendmsg+0x37/0x43 [ 2866.132281] [] xs_send_kvec+0x77/0x80 [ 2866.132281] [] xs_sendpages+0x6f/0x1a0 [ 2866.132281] [] ? try_to_del_timer_sync+0x55/0x61 [ 2866.132281] [] xs_tcp_send_request+0x55/0xf1 [ 2866.132281] [] xprt_transmit+0x89/0x1db [ 2866.132281] [] ? call_connect+0x3c/0x3c [ 2866.132281] [] call_transmit+0x1c5/0x20e [ 2866.132281] [] __rpc_execute+0x6f/0x225 [ 2866.132281] [] ? call_connect+0x3c/0x3c [ 2866.132281] [] rpc_async_schedule+0x28/0x34 [ 2866.132281] [] process_one_work+0x24d/0x47f [ 2866.132281] [] ? process_one_work+0x1de/0x47f [ 2866.132281] [] ? __rpc_execute+0x225/0x225 [ 2866.132281] [] worker_thread+0x236/0x317 [ 2866.132281] [] ? process_scheduled_works+0x2f/0x2f [ 2866.132281] [] kthread+0x9a/0xa2 [ 2866.132281] [] kernel_thread_helper+0x4/0x10 [ 2866.132281] [] ? retint_restore_args+0x13/0x13 [ 2866.132281] [] ? __init_kthread_worker+0x5a/0x5a [ 2866.132281] [] ? gs_change+0x13/0x13 [ 2866.308506] IPv4: Attempt to release TCP socket in state 1 ffff880019ec0000 [ 2866.309689] ============================================================================= [ 2866.310254] BUG TCP (Not tainted): Object already free [ 2866.310254] ----------------------------------------------------------------------------- [ 2866.310254] The bug comes from the fact that timer set in sk_reset_timer() can run before we actually do the sock_hold(). socket refcount reaches zero and we free the socket too soon. timer handler is not allowed to reduce socket refcnt if socket is owned by the user, or we need to change sk_reset_timer() implementation. We should take a reference on the socket in case TCP_DELACK_TIMER_DEFERRED or TCP_DELACK_TIMER_DEFERRED bit are set in tsq_flags Also fix a typo in tcp_delack_timer(), where TCP_WRITE_TIMER_DEFERRED was used instead of TCP_DELACK_TIMER_DEFERRED. For consistency, use same socket refcount change for TCP_MTU_REDUCED_DEFERRED, even if not fired from a timer. Reported-by: Fengguang Wu Tested-by: Fengguang Wu Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp_timer.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'net/ipv4/tcp_timer.c') diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index 6df36ad55a38..b774a03bd1dc 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -252,7 +252,8 @@ static void tcp_delack_timer(unsigned long data) inet_csk(sk)->icsk_ack.blocked = 1; NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); /* deleguate our work to tcp_release_cb() */ - set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags); + if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags)) + sock_hold(sk); } bh_unlock_sock(sk); sock_put(sk); @@ -481,7 +482,8 @@ static void tcp_write_timer(unsigned long data) tcp_write_timer_handler(sk); } else { /* deleguate our work to tcp_release_cb() */ - set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags); + if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags)) + sock_hold(sk); } bh_unlock_sock(sk); sock_put(sk); -- cgit v1.2.3