On Thu, Jul 01 2010 at 4:19pm -0400, James Bottomley <James.Bottomley@xxxxxxx> wrote: > On Thu, 2010-07-01 at 16:15 -0400, Mike Snitzer wrote: > > On Thu, Jul 01 2010 at 9:03am -0400, > > Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > > > > > On Thu, Jul 01 2010 at 6:49am -0400, > > > FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote: > > > > > > > This fixes discard page leak by using q->unprep_rq_fn facility. > > > > > > > > q->unprep_rq_fn is called when all the data buffer (req->bio and > > > > scsi_data_buffer) in the request is freed. > > > > > > > > sd_unprep() uses rq->buffer to free discard page allocated in > > > > sd_prepare_discard(). > > > > > > > > Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> > > > > > > Thanks for sorting this out Tomo, all 3 patches work great! > > > > > > BTW, there is one remaining (rare) leak in the allocation path. > > > > > > The following patch serves to fix it but I'm not sure if there is a more > > > elegant way to address this. > > > > I've continued to look at this to arrive at alternative implementation. > > Here is a summary of the problem: > > > > A 'scsi_setup_discard_cmnd' return other than BLKPREP_OK will not cause > > a discard request to get completely stripped down ('blk_finish_request' > > isn't calling 'blk_unprep_request' because REQ_DONTPREP is not set by > > 'scsi_prep_return' for none BLKPREP_OK return). Therefore the discard > > request's page will _not_ get cleaned up. > > > > Aside from code inspection, I confirmed this by adding some test code to > > force a one-time initial BLKPREP_DEFER return from > > 'scsi_setup_discard_cmnd'. > > > > > An alternative would be to check if the page is already allocated > > > (before allocating the page in scsi_setup_discard_cmnd)? > > > > Unfortunatey this "alternative" won't work because it completely ignores > > the case where BLKPREP_KILL is returned from scsi_setup_discard_cmnd'. > > > > > Please advise, thanks. > > > > In short, I'm not too happy that the following patch doesn't allow for > > centralized cleanup of the discard request's page (via sd_unprep_fn). > > But in order to do that we'd likely have to: > > 1) relax blk_finish_request's REQ_DONTPREP constraint > > 2) add other weird conditionals within blk_unprep_request because > > the discard request wasn't _really_ prepared? > > > > So given this I'm inclined to stick with the following patch. > > > > Jens and/or James, what do you think? > > The rules are pretty clear: Unprep is only called if the request gets > prepped ... that means you have to return BLKPREP_OK. Defer or kill > assume there's no teardown to do, so the allocation (if it took place) > must be reversed before returning them OK, thanks for clarifying. This confirms that the general approach I took in this patch is correct. It remains to be seen if Jens is agreeable with blk_clear_request_payload. I know Christoph thought my introduction and use of blk_clear_request_payload was reasonable. Christoph, please feel free to add your Ack to this patch if you approve. I look forward to feedback from Tomo and Jens now too. Hopefully Jens will pick this patch up. regards, Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel