On Wed, Sep 01 2010 at 3:15am -0400, Kiyoshi Ueda <k-ueda@xxxxxxxxxxxxx> wrote: > Hi Tejun, > > On 08/31/2010 12:45 AM +0900, Tejun Heo wrote: > > This patch converts request-based dm to support the new REQ_FLUSH/FUA. > > > > The original request-based flush implementation depended on > > request_queue blocking other requests while a barrier sequence is in > > progress, which is no longer true for the new REQ_FLUSH/FUA. > > > > In general, request-based dm doesn't have infrastructure for cloning > > one source request to multiple targets, but the original flush > > implementation had a special mostly independent path which can issue > > flushes to multiple targets and sequence them. However, the > > capability isn't currently in use and adds a lot of complexity. > > Moreoever, it's unlikely to be useful in its current form as it > > doesn't make sense to be able to send out flushes to multiple targets > > when write requests can't be. > > > > This patch rips out special flush code path and deals handles > > REQ_FLUSH/FUA requests the same way as other requests. The only > > special treatment is that REQ_FLUSH requests use the block address 0 > > when finding target, which is enough for now. > > > > * added BUG_ON(!dm_target_is_valid(ti)) in dm_request_fn() as > > suggested by Mike Snitzer > > Thank you for your work. > > I don't see any obvious problem on this patch. > However, I hit a NULL pointer dereference below when I use a mpath > device with barrier option of ext3. I'm investigating the cause now. > (Also I'm not sure the cause of the hang which Mike is hitting yet.) > > I tried on the commit 28dd53b26d362c16234249bad61db8cbd9222d0b of > git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git flush-fua. > > # mke2fs -j /dev/mapper/mpatha > # mount -o barrier=1 /dev/mapper/mpatha /mnt/0 > # dd if=/dev/zero of=/mnt/0/a bs=512 count=1 > # sync > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000078 FYI, I can't reproduce this using all of Tejun's latest patches (not yet in the flush-fua git tree). But I haven't tried the specific flush-fua commit that you referenced. Mike -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
