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From: Eric Dumazet <edumazet@google.com>
Date: Fri, 22 Jan 2016 23:06:44 -0800
Subject: [PATCH] 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 :
[306295.402231] NMI backtrace for cpu 1
[306295.402238] RIP: 0010:[<ffffffffa9804e95>] [<ffffffffa9804e95>] _raw_spin_lock+0x25/0x30
...
[306295.402255] Stack:
[306295.402256] ffff88407f023cb0 ffffffffa99cbdc3 ffff88407f023ca0 ffff88012f496bb0
[306295.402266] ffffffffaa4dc1f0 ffff8820d94f0dc0 000000000000000a ffffffffaa4b4280
[306295.402275] ffff88407f023ce0 ffffffffa98a21d0 ffff88407f023cc0 ffff88407f023ca0
[306295.402284] Call Trace:
[306295.402286] <IRQ>
[306295.402288]
[306295.402291] [<ffffffffa99cbdc3>] tcp_v6_rcv+0x243/0x620
[306295.402304] [<ffffffffa99c38af>] ip6_input_finish+0x11f/0x330
[306295.402309] [<ffffffffa99c3b38>] ip6_input+0x38/0x40
[306295.402313] [<ffffffffa99c3b7c>] ip6_rcv_finish+0x3c/0x90
[306295.402318] [<ffffffffa99c3e79>] ipv6_rcv+0x2a9/0x500
[306295.402323] [<ffffffffa989a1a1>] process_backlog+0x461/0xaa0
[306295.402332] [<ffffffffa9899a57>] net_rx_action+0x147/0x430
[306295.402337] [<ffffffffa980cca7>] __do_softirq+0x167/0x2d0
[306295.402341] [<ffffffffa9d912dc>] call_softirq+0x1c/0x30
[306295.402345] [<ffffffffa980687f>] do_softirq+0x3f/0x80
[306295.402350] [<ffffffffa980cf7e>] irq_exit+0x6e/0xc0
[306295.402355] [<ffffffffa980a5b5>] smp_call_function_single_interrupt+0x35/0x40
[306295.402360] [<ffffffffa9d90bfa>] call_function_single_interrupt+0x6a/0x70
[306295.402361] <EOI>
[306295.402364]
[306295.402376] [<ffffffffa9a3fa32>] printk+0x4d/0x4f
[306295.402390] [<ffffffffa99e1726>] printk_address+0x31/0x33
[306295.402395] [<ffffffffa99e175b>] print_trace_address+0x33/0x3c
[306295.402408] [<ffffffffa99e165b>] print_context_stack+0x7f/0x119
[306295.402412] [<ffffffffa99e07f1>] dump_trace+0x26b/0x28e
[306295.402417] [<ffffffffa99e17b3>] show_trace_log_lvl+0x4f/0x5c
[306295.402421] [<ffffffffa99e0a14>] show_stack_log_lvl+0x104/0x113
[306295.402425] [<ffffffffa99e1819>] show_stack+0x42/0x44
[306295.402429] [<ffffffffa9ba350a>] dump_stack+0x46/0x58
[306295.402434] [<ffffffffa9d0957d>] netdev_rx_csum_fault+0x38/0x3c
[306295.402439] [<ffffffffa9988e0e>] __skb_checksum_complete_head+0x6e/0x80
[306295.402444] [<ffffffffa9988e31>] __skb_checksum_complete+0x11/0x20
[306295.402449] [<ffffffffa98acf65>] tcp_rcv_established+0x2bd5/0x2fd0
[306295.402468] [<ffffffffa99cb69c>] tcp_v6_do_rcv+0x13c/0x620
[306295.402477] [<ffffffffa9984be5>] sk_backlog_rcv+0x15/0x30
[306295.402482] [<ffffffffa98931e2>] release_sock+0xd2/0x150
[306295.402486] [<ffffffffa98a51b1>] tcp_recvmsg+0x1c1/0xfc0
[306295.402491] [<ffffffffa98b637d>] inet_recvmsg+0x7d/0x90
[306295.402495] [<ffffffffa9891fcf>] sock_recvmsg+0xaf/0xe0
[306295.402505] [<ffffffffa9892611>] ___sys_recvmsg+0x111/0x3b0
[306295.402528] [<ffffffffa9892f5c>] SyS_recvmsg+0x5c/0xb0
[306295.402532] [<ffffffffa9d8fba2>] system_call_fastpath+0x16/0x1b
Fixes: b58d977432c8 ("dump_stack: serialize the output from dump_stack()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alex Thorlton <athorlton@sgi.com>
---
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -25,6 +25,7 @@ static atomic_t dump_lock = ATOMIC_INIT(
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(voi
* Permit this cpu to perform nested stack dumps while serialising
* against other CPUs
*/
- preempt_disable();
-
retry:
+ 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);
cpu_relax();
goto retry;
}
@@ -52,7 +53,7 @@ retry:
if (!was_locked)
atomic_set(&dump_lock, -1);
- preempt_enable();
+ local_irq_restore(flags);
}
#else
asmlinkage __visible void dump_stack(void)
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