Hi. The following reproducer causes auditd daemon hang up. (But the hang up is released after the audit_backlog_wait_time passes.) # auditctl -a exit,always -S all # reboot I reproduced the hangup on KVM, and then got a crash dump. After I analyzed the dump, I found auditd daemon hung up in audit_log_start. (I have confirmed it on linux-3.12-rc4.) Like this: crash> bt 1426 PID: 1426 TASK: ffff88007b63e040 CPU: 1 COMMAND: "auditd" #0 [ffff88007cb93918] __schedule at ffffffff8155d980 #1 [ffff88007cb939b0] schedule at ffffffff8155de99 #2 [ffff88007cb939c0] schedule_timeout at ffffffff8155b840 #3 [ffff88007cb93a60] audit_log_start at ffffffff810d3ce5 #4 [ffff88007cb93b20] audit_log_config_change at ffffffff810d3ece #5 [ffff88007cb93b60] audit_receive_msg at ffffffff810d4fd6 #6 [ffff88007cb93c00] audit_receive at ffffffff810d5173 #7 [ffff88007cb93c30] netlink_unicast at ffffffff814c5269 #8 [ffff88007cb93c90] netlink_sendmsg at ffffffff814c6386 #9 [ffff88007cb93d20] sock_sendmsg at ffffffff814813c0 #10 [ffff88007cb93e30] SYSC_sendto at ffffffff81481524 #11 [ffff88007cb93f70] sys_sendto at ffffffff8148157e #12 [ffff88007cb93f80] system_call_fastpath at ffffffff81568052 RIP: 00007f5c47f7fba3 RSP: 00007fffcf21a118 RFLAGS: 00010202 RAX: 000000000000002c RBX: ffffffff81568052 RCX: 0000000000000000 RDX: 0000000000000030 RSI: 00007fffcf21e7d0 RDI: 0000000000000003 RBP: 00007fffcf21e7d0 R8: 00007fffcf21a130 R9: 000000000000000c R10: 0000000000000000 R11: 0000000000000293 R12: ffffffff8148157e R13: ffff88007cb93f78 R14: 0000000000000020 R15: 0000000000000030 ORIG_RAX: 000000000000002c CS: 0033 SS: 002b The reason is that auditd daemon itself cannot consume its backlog while audit_log_start is calling schedule_timeout on auditd daemon. So, that is a deadlock! Therefore, I think audit_log_start shouldn't handle auditd's backlog when auditd daemon executes audit_log_start. For example, I made the following fix patch. -------------------------------------------------------------- auditd daemon can execute the audit_log_start, and then it can cause a hang up because only auditd daemon can consume the backlog. So, audit_log_start executed by auditd daemon should not handle the backlog in case auditd daemon hangs up (while wait_for_auditd is calling). Signed-off-by: Toshiyuki Okajima <toshi.okajima(a)jp.fujitsu.com&gt; --- kernel/audit.c | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-) diff --git a/kernel/audit.c b/kernel/audit.c index 7b0e23a..86c389e 100644 --- a/kernel/audit.c +++ b/kernel/audit.c @@ -1098,6 +1098,9 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask, int reserve; unsigned long timeout_start = jiffies; + if (audit_pid && (audit_pid == current->pid)) + return NULL; + if (audit_initialized != AUDIT_INITIALIZED) return NULL; -- 1.5.5.6