Messages in this thread Patch in this message | | | Date | Wed, 28 Aug 2013 18:21:14 -0400 | From | Luiz Capitulino <> | Subject | [RFC] audit: avoid soft lockup in audit_log_start() |
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I'm getting the following soft lockup:
CPU: 6 PID: 2278 Comm: killall5 Tainted: GF 3.11.0-rc7+ #1 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 0000000000000099 ffff88011fd83de8 ffffffff815324df 0000000000002800 ffffffff817d48f9 ffff88011fd83e68 ffffffff8152e669 ffff88011fd83e68 ffffffff00000008 ffff88011fd83e78 ffff88011fd83e18 0000004081dac040 Call Trace: <IRQ> [<ffffffff815324df>] dump_stack+0x46/0x58 [<ffffffff8152e669>] panic+0xbb/0x1c4 [<ffffffff810d03c3>] watchdog_timer_fn+0x163/0x170 [<ffffffff8106c691>] __run_hrtimer+0x81/0x1c0 [<ffffffff810d0260>] ? watchdog+0x30/0x30 [<ffffffff8106cea7>] hrtimer_interrupt+0x107/0x240 [<ffffffff8102f61b>] local_apic_timer_interrupt+0x3b/0x60 [<ffffffff81542465>] smp_apic_timer_interrupt+0x45/0x60 [<ffffffff8154124a>] apic_timer_interrupt+0x6a/0x70 <EOI> [<ffffffff810c2f5f>] ? audit_log_start+0xbf/0x430 [<ffffffff810c2fe7>] ? audit_log_start+0x147/0x430 [<ffffffff81079030>] ? try_to_wake_up+0x2a0/0x2a0 [<ffffffff810c86be>] audit_log_exit+0x6ae/0xc30 [<ffffffff81188662>] ? __alloc_fd+0x42/0x100 [<ffffffff810c98e7>] __audit_syscall_exit+0x257/0x2b0 [<ffffffff81540794>] sysret_audit+0x17/0x21
The reproducer is somewhat unusual:
1. Install RHEL6.5 (maybe a similar older user-space will do) 2. Boot the just installed system 3. In this first boot you'll meet the firstboot script, which will do some setup and (depending on your answers) it will reboot the machine 4. During that first reboot the system hangs while terminating all processes:
Sending all processes the TERM signal...
It's when the soft lockup above happens. And yes, I managed to get this with latest upstream kernel (HEAD fa8218def1b1)
I'm reproducing it on a VM, but the first report was on bare-metal.
This is what is happening:
1. audit_log_start() is called 2. As we have SKBs waiting in audit_skb_queue and all conditions evaluate to true, we sleep in wait_for_auditd() 3. Go to 2, until sleep_time gets negative and audit_log_start() just busy-waits
Now, *why* this is happening is a mistery to me. I tried debugging it, but all I could find is that at some point the kauditd thread never wakes up after having called schedule(). I even tried waking it up before calling wait_for_auditd(), but it didn't.
This patch is a RFC because it doesn't actually fix anything. It just bails out before we busy-wait. Which is better than nothing, but the system will still give a long pause when terminating all processes. Besides, we risk papering over the real bug...
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com> --- kernel/audit.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/kernel/audit.c b/kernel/audit.c index 91e53d0..33e9c4c 100644 --- a/kernel/audit.c +++ b/kernel/audit.c @@ -1097,6 +1097,7 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask, unsigned int uninitialized_var(serial); int reserve; unsigned long timeout_start = jiffies; + unsigned long sleep_time; if (audit_initialized != AUDIT_INITIALIZED) return NULL; @@ -1112,13 +1113,11 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask, while (audit_backlog_limit && skb_queue_len(&audit_skb_queue) > audit_backlog_limit + reserve) { - if (gfp_mask & __GFP_WAIT && audit_backlog_wait_time) { - unsigned long sleep_time; - sleep_time = timeout_start + audit_backlog_wait_time - jiffies; - if ((long)sleep_time > 0) - wait_for_auditd(sleep_time); + if (gfp_mask & __GFP_WAIT && audit_backlog_wait_time + && sleep_time > 0) { + wait_for_auditd(sleep_time); continue; } if (audit_rate_check() && printk_ratelimit()) -- 1.8.1.4
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