lkml.org 
[lkml]   [2020]   [Jun]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/6] sched: TTWU, IPI, and assorted stuff
On Mon, Jun 15, 2020 at 02:56:54PM +0200, Peter Zijlstra wrote:
> Hi,
>
> So Paul reported rcutorture hitting a NULL dereference, and patch #1 fixes it.
>
> Now, patch #1 is obviously correct, but I can't explain how exactly it leads to
> the observed NULL pointer dereference. The NULL pointer deref happens in
> find_matching_se()'s last while() loop when is_same_group() fails even though
> both parents are NULL.

My bisection of yet another bug sometimes hits the scheduler NULL pointer
dereference on older commits. I will try out patch #2.

Whether this is reassuring or depressing, I have no idea. :-/

> The only explanation I have for that is that we just did an activate_task()
> while: 'task_cpu(p) != cpu_of(rq)', because then 'p->se.cfs_rq' doesn't match.
> However, I can't see how the lack of #1 would lead to that. Never-the-less,
> patch #2 adds assertions to warn us of this case.
>
> Patch #3 is a trivial rename that ought to eradicate some confusion.
>
> The last 3 patches is what I ended up with for cleaning up the whole
> smp_call_function/irq_work/ttwu thing more.

Would it be possible to allow a target CPU # on those instances of
__call_single_data? This is extremely helpful for debugging lost
smp_call_function*() calls.

Thanx, Paul

\
 
 \ /
  Last update: 2020-06-15 18:23    [W:0.186 / U:1.724 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site