audit: Two efficiency fixes for audit mechanism
author: Dan Duval <dan.du...@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.du...@oracle.com>
Signed-off-by: Chuck Anderson <chuck.ander...@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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
