path: root/lib/dump_stack.c
diff options
authorEric Dumazet <>2016-02-05 15:36:16 -0800
committerLinus Torvalds <>2016-02-05 18:10:40 -0800
commitd7ce36924344ace0dbdc855b1206cacc46b36d45 (patch)
tree7c40a3bd87e880763f3ee512953a173721701e3d /lib/dump_stack.c
parentacf128d048c76aeaa99646bce3488d73be215f70 (diff)
dump_stack: avoid potential deadlocks
Some servers experienced fatal deadlocks because of a combination of bugs, leading to multiple cpus calling dump_stack(). The checksumming bug was fixed in commit 34ae6a1aa054 ("ipv6: update skb->csum when CE mark is propagated"). The second problem is a faulty locking in dump_stack() CPU1 runs in process context and calls dump_stack(), grabs dump_lock. CPU2 receives a TCP packet under softirq, grabs socket spinlock, and call dump_stack() from netdev_rx_csum_fault(). dump_stack() spins on atomic_cmpxchg(&dump_lock, -1, 2), since dump_lock is owned by CPU1 While dumping its stack, CPU1 is interrupted by a softirq, and happens to process a packet for the TCP socket locked by CPU2. CPU1 spins forever in spin_lock() : deadlock Stack trace on CPU1 looked like : NMI backtrace for cpu 1 RIP: _raw_spin_lock+0x25/0x30 ... Call Trace: <IRQ> tcp_v6_rcv+0x243/0x620 ip6_input_finish+0x11f/0x330 ip6_input+0x38/0x40 ip6_rcv_finish+0x3c/0x90 ipv6_rcv+0x2a9/0x500 process_backlog+0x461/0xaa0 net_rx_action+0x147/0x430 __do_softirq+0x167/0x2d0 call_softirq+0x1c/0x30 do_softirq+0x3f/0x80 irq_exit+0x6e/0xc0 smp_call_function_single_interrupt+0x35/0x40 call_function_single_interrupt+0x6a/0x70 <EOI> printk+0x4d/0x4f printk_address+0x31/0x33 print_trace_address+0x33/0x3c print_context_stack+0x7f/0x119 dump_trace+0x26b/0x28e show_trace_log_lvl+0x4f/0x5c show_stack_log_lvl+0x104/0x113 show_stack+0x42/0x44 dump_stack+0x46/0x58 netdev_rx_csum_fault+0x38/0x3c __skb_checksum_complete_head+0x6e/0x80 __skb_checksum_complete+0x11/0x20 tcp_rcv_established+0x2bd5/0x2fd0 tcp_v6_do_rcv+0x13c/0x620 sk_backlog_rcv+0x15/0x30 release_sock+0xd2/0x150 tcp_recvmsg+0x1c1/0xfc0 inet_recvmsg+0x7d/0x90 sock_recvmsg+0xaf/0xe0 ___sys_recvmsg+0x111/0x3b0 SyS_recvmsg+0x5c/0xb0 system_call_fastpath+0x16/0x1b Fixes: b58d977432c8 ("dump_stack: serialize the output from dump_stack()") Signed-off-by: Eric Dumazet <> Cc: Alex Thorlton <> Cc: <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'lib/dump_stack.c')
1 files changed, 4 insertions, 3 deletions
diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index 6745c6230db3..c30d07e99dba 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -25,6 +25,7 @@ static atomic_t dump_lock = ATOMIC_INIT(-1);
asmlinkage __visible void dump_stack(void)
+ unsigned long flags;
int was_locked;
int old;
int cpu;
@@ -33,9 +34,8 @@ asmlinkage __visible void dump_stack(void)
* Permit this cpu to perform nested stack dumps while serialising
* against other CPUs
- preempt_disable();
+ local_irq_save(flags);
cpu = smp_processor_id();
old = atomic_cmpxchg(&dump_lock, -1, cpu);
if (old == -1) {
@@ -43,6 +43,7 @@ retry:
} else if (old == cpu) {
was_locked = 1;
} else {
+ local_irq_restore(flags);
goto retry;
@@ -52,7 +53,7 @@ retry:
if (!was_locked)
atomic_set(&dump_lock, -1);
- preempt_enable();
+ local_irq_restore(flags);
asmlinkage __visible void dump_stack(void)