[Cluster-devel] [GFS2 PATCH 1/2] GFS2: Make gfs2_clear_inode() queue the final put

[Steven Whitehouse <swhiteho@redhat.com>]

Hi,

On 08/12/15 07:57, Dave Chinner wrote:
> On Wed, Dec 02, 2015 at 11:42:13AM -0500, Bob Peterson wrote:
>> ----- Original Message -----
>> (snip)
>>> Please take a look at this
>>> again and figure out what the problematic cycle of events is, and then
>>> work out how to avoid that happening in the first place. There is no
>>> point in replacing one problem with another one, particularly one which
>>> would likely be very tricky to debug,
>>>
>>> Steve.
>> Rhe problematic cycle of events is well known:
>> gfs2_clear_inode calls gfs2_glock_put() for the inode's glock,
>> but if it's the very last put, it calls into dlm, which can block,
>> and that's where we get into trouble.
>>
>> The livelock goes like this:
>>
>> 1. A fence operation needs memory, so it blocks on memory allocation.
>> 2. Memory allocation blocks on slab shrinker.
>> 3. Slab shrinker calls into vfs inode shrinker to free inodes from memory.
> ....
>> 7. dlm blocks on a pending fence operation. Goto 1.
> Therefore, the fence operation should be doing GFP_NOFS allocations
> to prevent re-entry into the DLM via the filesystem via the shrinker....
>
> Cheers,
>
> Dave.

Which would be ideal, but how do you do that from user space?

Steve.