lkml.org 
[lkml]   [2019]   [Aug]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RT PATCH 3/3] hrtimer: Prevent using uninitialized spin_lock in hrtimer_grab_expiry_lock()
On Wed, 21 Aug 2019, Julien Grall wrote:

> migration_base is used as a placeholder when an hrtimer is switching
> between base (see switch_hrtimer_timer_base). It is possible
> theoritically possible to have timer->base equal to migration_base.
>
> Even if it is a placeholder, it would pass all the current check in
> hrtimer_grab_expiry_lock() leading to use softirq_expiry_lock
> uninitialized.
>
> This is can be prevented by checking whether the base is equal to
> the placeholder (i.e. migration_base).

That's a lame argument. The point is that it does not make sense to do that
on migration base, but not for the reason you are giving (uninitialized
lock).

If base == migration_base then there is no point to lock soft_expiry_lock
simply because the timer is not executing the callback in soft irq context
and the whole lock/unlock dance can be avoided.

But, yes. Good catch.

Thanks,

tglx

\
 
 \ /
  Last update: 2019-08-21 16:03    [W:0.183 / U:3.784 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site