lkml.org 
[lkml]   [2015]   [Apr]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] qrwlock: Fix bug in interrupt handling code
On Thu, Apr 09, 2015 at 04:07:55PM -0400, Waiman Long wrote:
> The qrwlock is fair in the process context, but becoming unfair when
> in the interrupt context to support use cases like the tasklist_lock.
> However, the unfair code in the interrupt context has problem that
> may cause deadlock.
>
> The fast path increments the reader count. In the interrupt context,
> the reader in the slowpath will wait until the writer release the
> lock. However, if other readers have the lock and the writer is just
> in the waiting mode. It will never get the write lock because the
> that interrupt context reader has increment the count. This will
> cause deadlock.
>
> This patch fixes this problem by checking the state of the
> reader/writer count retrieved at the fast path. If the writer
> is in waiting mode, the reader will get the lock immediately and
> return. Otherwise, it will wait until the writer release the lock
> like before.

A little word on how you found this issue would be nice.

I'll have a look at the actual patch tomorrow, my brain is properly
fried (as demonstrated by my last email to you ;-).


\
 
 \ /
  Last update: 2015-04-09 22:41    [W:0.053 / U:7.812 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site