Commit Graph

8 Commits

Author SHA1 Message Date
Anton Blanchard e5af022616 softlockup: Fix hung_task_check_count sysctl
I'm seeing spikes of up to 0.5ms in khungtaskd on a large
machine. To reduce this source of jitter I tried setting
hung_task_check_count to 0:

 # echo 0 > /proc/sys/kernel/hung_task_check_count

which didn't have the intended response. Change to a post
increment of max_count, so a value of 0 means check 0 tasks.

Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: msb@google.com
LKML-Reference: <20091127022820.GU32182@kryten>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-11-27 06:21:57 +01:00
Alexey Dobriyan 8d65af789f sysctl: remove "struct file *" argument of ->proc_handler
It's unused.

It isn't needed -- read or write flag is already passed and sysctl
shouldn't care about the rest.

It _was_ used in two places at arch/frv for some reason.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-24 07:21:04 -07:00
Frederic Weisbecker cf2592f59c softlockup: ensure the task has been switched out once
When we check if a task has been switched out since the last scan, we might
have a race condition on the following scenario:

- the task is freshly created and scheduled

- it puts its state to TASK_UNINTERRUPTIBLE and is not yet switched out

- check_hung_task() scans this task and will report a false positive because
  t->nvcsw + t->nivcsw == t->last_switch_count == 0

Add a check for such cases.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-11 11:04:16 +01:00
Mandeep Singh Baines 17406b82d6 softlockup: remove timestamp checking from hung_task
Impact: saves sizeof(long) bytes per task_struct

By guaranteeing that sysctl_hung_task_timeout_secs have elapsed between
tasklist scans we can avoid using timestamps.

Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-09 11:03:49 +01:00
Mandeep Singh Baines 94be52dc07 softlockup: convert read_lock in hung_task to rcu_read_lock
Since the tasklist is protected by rcu list operations, it is safe
to convert the read_lock()s to rcu_read_lock().

Suggested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-05 19:55:31 +01:00
Mandeep Singh Baines ce9dbe244b softlockup: check all tasks in hung_task
Impact: extend the scope of hung-task checks

Changed the default value of hung_task_check_count to PID_MAX_LIMIT.
hung_task_batch_count added to put an upper bound on the critical
section. Every hung_task_batch_count checks, the rcu lock is never
held for a too long time.

Keeping the critical section small minimizes time preemption is disabled
and keeps rcu grace periods small.

To prevent following a stale pointer, get_task_struct is called on g and t.
To verify that g and t have not been unhashed while outside the critical
section, the task states are checked.

The design was proposed by Frédéric Weisbecker.

Signed-off-by: Mandeep Singh Baines <msb@google.com>
Suggested-by: Frédéric Weisbecker <fweisbec@gmail.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-05 19:54:57 +01:00
Mandeep Singh Baines 603a148f43 softlockup: fix potential race in hung_task when resetting timeout
Impact: fix potential false panic

A potential race exists if sysctl_hung_task_timeout_secs is reset to 0
while inside check_hung_uniterruptible_tasks(). If check_task() is
entered, a comparison with 0 will result in a false hung_task being
detected.

If sysctl_hung_task_panic is set, the system will panic.

Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-18 19:20:17 +01:00
Mandeep Singh Baines e162b39a36 softlockup: decouple hung tasks check from softlockup detection
Decoupling allows:

* hung tasks check to happen at very low priority

* hung tasks check and softlockup to be enabled/disabled independently
  at compile and/or run-time

* individual panic settings to be enabled disabled independently
  at compile and/or run-time

* softlockup threshold to be reduced without increasing hung tasks
  poll frequency (hung task check is expensive relative to softlock watchdog)

* hung task check to be zero over-head when disabled at run-time

Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-16 14:06:04 +01:00