Messages in this thread Patch in this message | | | Date | Mon, 02 Sep 2013 20:53:47 -0700 | From | Chuck Anderson <> | Subject | [PATCH 2/2] audit: Two efficiency fixes for audit mechanism |
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audit: Two efficiency fixes for audit mechanism
author: Dan Duval <dan.duval@oracle.com>
These and similar errors were seen on a patched 3.8 kernel when the audit subsystem was overrun during boot:
udevd[876]: worker [887] unexpectedly returned with status 0x0100 udevd[876]: worker [887] failed while handling '/devices/pci0000:00/0000:00:03.0/0000:40:00.0' udevd[876]: worker [880] unexpectedly returned with status 0x0100 udevd[876]: worker [880] failed while handling '/devices/LNXSYSTM:00/LNXPWRBN:00/input/input1/event1'
udevadm settle - timeout of 180 seconds reached, the event queue contains: /sys/devices/LNXSYSTM:00/LNXPWRBN:00/input/input1/event1 (3995) /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/INT3F0D:00 (4034)
audit: audit_backlog=258 > audit_backlog_limit=256 audit: audit_lost=1 audit_rate_limit=0 audit_backlog_limit=256
The changes below increase the efficiency of the audit code and prevent it from being overrun:
1. Only issue a wake_up in kauditd if the length of the skb queue is less than the backlog limit. Otherwise, threads waiting in wait_for_auditd() will simply wake up, discover that the queue is still too long for them to proceed, and go back to sleep. This results in wasted context switches and machine cycles. kauditd_thread() is the only function that removes buffers from audit_skb_queue so we can't race. If we did, the timeout in wait_for_auditd() would expire and the waiting thread would continue.
2. Use add_wait_queue_exclusive() in wait_for_auditd() to put the thread on the wait queue. When kauditd dequeues an skb, all of the waiting threads are waiting for the same resource, but only one is going to get it, so there's no need to wake up more than one waiter.
Signed-off-by: Dan Duval <dan.duval@oracle.com> Signed-off-by: Chuck Anderson <chuck.anderson@oracle.com> --- kernel/audit.c | 7 +++++-- 1 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/audit.c b/kernel/audit.c index 9a78dde..d87b4dd 100644 --- a/kernel/audit.c +++ b/kernel/audit.c @@ -449,8 +449,11 @@ static int kauditd_thread(void *dummy) flush_hold_queue();
skb = skb_dequeue(&audit_skb_queue); - wake_up(&audit_backlog_wait); + if (skb) { + if(skb_queue_len(&audit_skb_queue) <= audit_backlog_limi t) + wake_up(&audit_backlog_wait); + if (audit_pid) kauditd_send_skb(skb); else @@ -1059,7 +1062,7 @@ static void wait_for_auditd(unsigned long sleep_time, int limit) { DECLARE_WAITQUEUE(wait, current); set_current_state(TASK_UNINTERRUPTIBLE); - add_wait_queue(&audit_backlog_wait, &wait); + add_wait_queue_exclusive(&audit_backlog_wait, &wait);
if (audit_backlog_limit && skb_queue_len(&audit_skb_queue) > limit) -- 1.7.1
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