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author | Oleg Nesterov <oleg@redhat.com> | 2012-03-05 14:59:14 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-03-05 15:49:42 -0800 |
commit | 6027ce497d44dd8eae1a9215789df178f6b422cc (patch) | |
tree | 5844f0d3899a7a3214cb1145b3d9a8f9660dd7c7 /.gitignore | |
parent | 6e27f63edbd7ab893258e16500171dd1270a1369 (diff) | |
download | op-kernel-dev-6027ce497d44dd8eae1a9215789df178f6b422cc.zip op-kernel-dev-6027ce497d44dd8eae1a9215789df178f6b422cc.tar.gz |
hung_task: fix the broken rcu_lock_break() logic
check_hung_uninterruptible_tasks()->rcu_lock_break() introduced by
"softlockup: check all tasks in hung_task" commit ce9dbe24 looks
absolutely wrong.
- rcu_lock_break() does put_task_struct(). If the task has exited
it is not safe to even read its ->state, nothing protects this
task_struct.
- The TASK_DEAD checks are wrong too. Contrary to the comment, we
can't use it to check if the task was unhashed. It can be unhashed
without TASK_DEAD, or it can be valid with TASK_DEAD.
For example, an autoreaping task can do release_task(current)
long before it sets TASK_DEAD in do_exit().
Or, a zombie task can have ->state == TASK_DEAD but release_task()
was not called, and in this case we must not break the loop.
Change this code to check pid_alive() instead, and do this before we drop
the reference to the task_struct.
Note: while_each_thread() under rcu_read_lock() is not really safe, it can
livelock. This will be fixed later, but fortunately in this case the
"max_count" logic saves us anyway.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Mandeep Singh Baines <msb@google.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to '.gitignore')
0 files changed, 0 insertions, 0 deletions