Re: soft lockup - CPU#0 stuck - Kernel 3.17.2

[Chris Mason <clm@fb.com>]

On Fri, Nov 21, 2014 at 8:01 AM, Patrick Schmid <schmid@phys.ethz.ch> 
wrote:
> On 15.11.2014 00:47, Chris Mason wrote:
>> 
>>  Ok, I think this is related to the new fair read/writer lock
>>  implementation in the generic kernel code.  
>> btrfs_clear_path_blocking()
>>  will end up taking locks outside of the strict locking order the 
>> rest
>>  of Btrfs uses.  This used to be fine because we hold the blocking 
>> lock
>>  while we do it, but with the new queued locks we're running into
>>  trouble.  We hit a similar bug earlier and I convinced myself the
>>  problem was only with btrfs_next_leaf and our trylock.  But it's a
>>  bigger problem than I realized.
>> 
>>  So for now I've changed btrfs_clear_path_blocking to honor the rules
>>  and fixed up our trylock to make it faster.
>> 
>>  I'm letting a test run on this patch over the weekend, since I don't
>>  want any surprises with your backup farm.
>> 
>>  -chris
> 
> Hi Chris
> 
> Here comes a short feedback.... I applied your patch (Fix lockups from
> btrfs_clear_path_blocking) yesterday and my system survived this 
> night! ;-)
> 
> Thank you for the quick fix.

Great to hear, thanks for following up.  I'm sending this to Linus for 
the next 3.18 rc.

-chris