Re: [PATCH 1/3] [PATCH i386] during VM oom condition, kill all threads in process group

Will Schmidt [off-list ref] writes:

On Fri, 2007-06-08 at 12:32 -0700, Andrew Morton wrote:

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On Fri, 08 Jun 2007 14:19:18 -0500
Will Schmidt [off-list ref] wrote:

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zap_other_threads() requires tasklist_lock.

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In fact, it's probably the case that rcu_read_lock() is now sufficient
locking coverage for zap_other_threads() (cc's people).

It had better be, because do_group_exit() forgot to take tasklist_lock.  It
is perhaps relying upon spin_lock()'s hidden rcu_read_lock() properties
without so much as a code comment, which would be somewhat nasty of it.

quoted

You could perhaps just call do_group_exit() from within the fault
handler,
btw.

Yup, so looks like I can actually replace the existing do_exit() call
with do_group_exit().   I'll sit on this for a bit to give other folks a
chance to comment on which lock call is sufficient, read_lock() or
rcu_read_lock(), etc;  and do_group_exit()'s issue with taking
tasklist_lock. 

No.  The rcu_read_lock is not sufficient.
Yes.  sighand->siglock is enough, and we explicitly take it in
do_group_exit before calling zap_other_threads.

Unless I have completely miss-understood this thread.

Eric

On 06/08, Eric W. Biederman wrote:

Will Schmidt [off-list ref] writes:

quoted

On Fri, 2007-06-08 at 12:32 -0700, Andrew Morton wrote:

quoted

On Fri, 08 Jun 2007 14:19:18 -0500
Will Schmidt [off-list ref] wrote:

quoted

quoted

quoted

quoted

zap_other_threads() requires tasklist_lock.

quoted

In fact, it's probably the case that rcu_read_lock() is now sufficient
locking coverage for zap_other_threads() (cc's people).

It had better be, because do_group_exit() forgot to take tasklist_lock.  It
is perhaps relying upon spin_lock()'s hidden rcu_read_lock() properties
without so much as a code comment, which would be somewhat nasty of it.

quoted

You could perhaps just call do_group_exit() from within the fault
handler,
btw.

Yup, so looks like I can actually replace the existing do_exit() call
with do_group_exit().   I'll sit on this for a bit to give other folks a
chance to comment on which lock call is sufficient, read_lock() or
rcu_read_lock(), etc;  and do_group_exit()'s issue with taking
tasklist_lock. 

No.  The rcu_read_lock is not sufficient.
Yes.  sighand->siglock is enough, and we explicitly take it in
do_group_exit before calling zap_other_threads.

Yes, we don't need tasklist_lock (or rcu_read_lock).

de_thread() calls zap_other_threads() under tasklist_lock, but this
is because we can change child_reaper.

Oleg.