| Message ID | 20200213123728.61216-2-pasic@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | virtio-blk: improve handling of DMA mapping failures | expand |
Hi Halil, When swiotlb full is hit for virtio_blk, there is below warning for once (the warning is not by this patch set). Is this expected or just false positive? [ 54.767257] virtio-pci 0000:00:04.0: swiotlb buffer is full (sz: 16 bytes), total 32768 (slots), used 258 (slots) [ 54.767260] virtio-pci 0000:00:04.0: overflow 0x0000000075770110+16 of DMA mask ffffffffffffffff bus limit 0 [ 54.769192] ------------[ cut here ]------------ [ 54.769200] WARNING: CPU: 3 PID: 102 at kernel/dma/direct.c:35 report_addr+0x71/0x77 [ 54.769200] Modules linked in: [ 54.769203] CPU: 3 PID: 102 Comm: kworker/u8:2 Not tainted 5.6.0-rc1+ #2 [ 54.769204] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 [ 54.769208] Workqueue: writeback wb_workfn (flush-253:0) [ 54.769211] RIP: 0010:report_addr+0x71/0x77 ... ... [ 54.769226] Call Trace: [ 54.769241] dma_direct_map_page+0xc9/0xe0 [ 54.769245] virtqueue_add+0x172/0xaa0 [ 54.769248] virtqueue_add_sgs+0x85/0xa0 [ 54.769251] virtio_queue_rq+0x292/0x480 [ 54.769255] __blk_mq_try_issue_directly+0x13e/0x1f0 [ 54.769257] blk_mq_request_issue_directly+0x48/0xa0 [ 54.769259] blk_mq_try_issue_list_directly+0x3c/0xb0 [ 54.769261] blk_mq_sched_insert_requests+0xb6/0x100 [ 54.769263] blk_mq_flush_plug_list+0x146/0x210 [ 54.769264] blk_flush_plug_list+0xba/0xe0 [ 54.769266] blk_mq_make_request+0x331/0x5b0 [ 54.769268] generic_make_request+0x10d/0x2e0 [ 54.769270] submit_bio+0x69/0x130 [ 54.769273] ext4_io_submit+0x44/0x50 [ 54.769275] ext4_writepages+0x56f/0xd30 [ 54.769278] ? cpumask_next_and+0x19/0x20 [ 54.769280] ? find_busiest_group+0x11a/0xa40 [ 54.769283] do_writepages+0x15/0x70 [ 54.769288] __writeback_single_inode+0x38/0x330 [ 54.769290] writeback_sb_inodes+0x219/0x4c0 [ 54.769292] __writeback_inodes_wb+0x82/0xb0 [ 54.769293] wb_writeback+0x267/0x300 [ 54.769295] wb_workfn+0x1aa/0x430 [ 54.769298] process_one_work+0x156/0x360 [ 54.769299] worker_thread+0x41/0x3b0 [ 54.769300] kthread+0xf3/0x130 [ 54.769302] ? process_one_work+0x360/0x360 [ 54.769303] ? kthread_bind+0x10/0x10 [ 54.769305] ret_from_fork+0x35/0x40 [ 54.769307] ---[ end trace 923a87a9ce0e777a ]--- Thank you very much! Dongli Zhang On 2/13/20 4:37 AM, Halil Pasic wrote: > Since nobody else is going to restart our hw_queue for us, the > blk_mq_start_stopped_hw_queues() is in virtblk_done() is not sufficient > necessarily sufficient to ensure that the queue will get started again. > In case of global resource outage (-ENOMEM because mapping failure, > because of swiotlb full) our virtqueue may be empty and we can get > stuck with a stopped hw_queue. > > Let us not stop the queue on arbitrary errors, but only on -EONSPC which > indicates a full virtqueue, where the hw_queue is guaranteed to get > started by virtblk_done() before when it makes sense to carry on > submitting requests. Let us also remove a stale comment. > > Signed-off-by: Halil Pasic <pasic@linux.ibm.com> > Cc: Jens Axboe <axboe@kernel.dk> > Fixes: f7728002c1c7 ("virtio_ring: fix return code on DMA mapping fails") > --- > > I'm in doubt with regards to the Fixes tag. The thing is, virtio-blk > probably made an assumption on virtqueue_add: the failure is either > because the virtqueue is full, or the failure is fatal. In both cases it > seems acceptable to stop the queue, although the fatal case is arguable. > Since commit f7728002c1c7 it the dma mapping has failed returns -ENOMEM > and not -EIO, and thus we have a recoverable failure that ain't > virtqueue full. So I lean towards to a fixes tag that references that > commit, although it ain't broken. Alternatively one could say 'Fixes: > e467cde23818 ("Block driver using virtio.")', if the aforementioned > assumption shouldn't have made in the first place. > --- > drivers/block/virtio_blk.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > index 54158766334b..adfe43f5ffe4 100644 > --- a/drivers/block/virtio_blk.c > +++ b/drivers/block/virtio_blk.c > @@ -245,10 +245,12 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, > err = virtblk_add_req(vblk->vqs[qid].vq, vbr, vbr->sg, num); > if (err) { > virtqueue_kick(vblk->vqs[qid].vq); > - blk_mq_stop_hw_queue(hctx); > + /* Don't stop the queue if -ENOMEM: we may have failed to > + * bounce the buffer due to global resource outage. > + */ > + if (err == -ENOSPC) > + blk_mq_stop_hw_queue(hctx); > spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags); > - /* Out of mem doesn't actually happen, since we fall back > - * to direct descriptors */ > if (err == -ENOMEM || err == -ENOSPC) > return BLK_STS_DEV_RESOURCE; > return BLK_STS_IOERR; >
On Fri, 14 Feb 2020 10:20:44 -0800 dongli.zhang@oracle.com wrote: > Hi Halil, > > When swiotlb full is hit for virtio_blk, there is below warning for once (the > warning is not by this patch set). Is this expected or just false positive? The warning is kind of expected. Certainly not a false positive, but it probably looks more dramatic than I would like it to look. If swiotlb cmdline parameter can be chosen so that the swiotlb won't run out of space, that is certainly preferable. But out of swiotlb space should merely result in performance degradation (provided the device drivers properly handle the condition). Thanks for having a look! Regards, Halil > > [ 54.767257] virtio-pci 0000:00:04.0: swiotlb buffer is full (sz: 16 bytes), > total 32768 (slots), used 258 (slots) > [ 54.767260] virtio-pci 0000:00:04.0: overflow 0x0000000075770110+16 of DMA > mask ffffffffffffffff bus limit 0 > [ 54.769192] ------------[ cut here ]------------ > [ 54.769200] WARNING: CPU: 3 PID: 102 at kernel/dma/direct.c:35 > report_addr+0x71/0x77 > [ 54.769200] Modules linked in: > [ 54.769203] CPU: 3 PID: 102 Comm: kworker/u8:2 Not tainted 5.6.0-rc1+ #2 > [ 54.769204] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 > [ 54.769208] Workqueue: writeback wb_workfn (flush-253:0) > [ 54.769211] RIP: 0010:report_addr+0x71/0x77 > ... ... > [ 54.769226] Call Trace: > [ 54.769241] dma_direct_map_page+0xc9/0xe0 > [ 54.769245] virtqueue_add+0x172/0xaa0 > [ 54.769248] virtqueue_add_sgs+0x85/0xa0 > [ 54.769251] virtio_queue_rq+0x292/0x480 > [ 54.769255] __blk_mq_try_issue_directly+0x13e/0x1f0 > [ 54.769257] blk_mq_request_issue_directly+0x48/0xa0 > [ 54.769259] blk_mq_try_issue_list_directly+0x3c/0xb0 > [ 54.769261] blk_mq_sched_insert_requests+0xb6/0x100 > [ 54.769263] blk_mq_flush_plug_list+0x146/0x210 > [ 54.769264] blk_flush_plug_list+0xba/0xe0 > [ 54.769266] blk_mq_make_request+0x331/0x5b0 > [ 54.769268] generic_make_request+0x10d/0x2e0 > [ 54.769270] submit_bio+0x69/0x130 > [ 54.769273] ext4_io_submit+0x44/0x50 > [ 54.769275] ext4_writepages+0x56f/0xd30 > [ 54.769278] ? cpumask_next_and+0x19/0x20 > [ 54.769280] ? find_busiest_group+0x11a/0xa40 > [ 54.769283] do_writepages+0x15/0x70 > [ 54.769288] __writeback_single_inode+0x38/0x330 > [ 54.769290] writeback_sb_inodes+0x219/0x4c0 > [ 54.769292] __writeback_inodes_wb+0x82/0xb0 > [ 54.769293] wb_writeback+0x267/0x300 > [ 54.769295] wb_workfn+0x1aa/0x430 > [ 54.769298] process_one_work+0x156/0x360 > [ 54.769299] worker_thread+0x41/0x3b0 > [ 54.769300] kthread+0xf3/0x130 > [ 54.769302] ? process_one_work+0x360/0x360 > [ 54.769303] ? kthread_bind+0x10/0x10 > [ 54.769305] ret_from_fork+0x35/0x40 > [ 54.769307] ---[ end trace 923a87a9ce0e777a ]--- > > Thank you very much! > > Dongli Zhang > > On 2/13/20 4:37 AM, Halil Pasic wrote: > > Since nobody else is going to restart our hw_queue for us, the > > blk_mq_start_stopped_hw_queues() is in virtblk_done() is not sufficient > > necessarily sufficient to ensure that the queue will get started again. > > In case of global resource outage (-ENOMEM because mapping failure, > > because of swiotlb full) our virtqueue may be empty and we can get > > stuck with a stopped hw_queue. > > > > Let us not stop the queue on arbitrary errors, but only on -EONSPC which > > indicates a full virtqueue, where the hw_queue is guaranteed to get > > started by virtblk_done() before when it makes sense to carry on > > submitting requests. Let us also remove a stale comment. > > > > Signed-off-by: Halil Pasic <pasic@linux.ibm.com> > > Cc: Jens Axboe <axboe@kernel.dk> > > Fixes: f7728002c1c7 ("virtio_ring: fix return code on DMA mapping fails") > > --- > > > > I'm in doubt with regards to the Fixes tag. The thing is, virtio-blk > > probably made an assumption on virtqueue_add: the failure is either > > because the virtqueue is full, or the failure is fatal. In both cases it > > seems acceptable to stop the queue, although the fatal case is arguable. > > Since commit f7728002c1c7 it the dma mapping has failed returns -ENOMEM > > and not -EIO, and thus we have a recoverable failure that ain't > > virtqueue full. So I lean towards to a fixes tag that references that > > commit, although it ain't broken. Alternatively one could say 'Fixes: > > e467cde23818 ("Block driver using virtio.")', if the aforementioned > > assumption shouldn't have made in the first place. > > --- > > drivers/block/virtio_blk.c | 8 +++++--- > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > > index 54158766334b..adfe43f5ffe4 100644 > > --- a/drivers/block/virtio_blk.c > > +++ b/drivers/block/virtio_blk.c > > @@ -245,10 +245,12 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, > > err = virtblk_add_req(vblk->vqs[qid].vq, vbr, vbr->sg, num); > > if (err) { > > virtqueue_kick(vblk->vqs[qid].vq); > > - blk_mq_stop_hw_queue(hctx); > > + /* Don't stop the queue if -ENOMEM: we may have failed to > > + * bounce the buffer due to global resource outage. > > + */ > > + if (err == -ENOSPC) > > + blk_mq_stop_hw_queue(hctx); > > spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags); > > - /* Out of mem doesn't actually happen, since we fall back > > - * to direct descriptors */ > > if (err == -ENOMEM || err == -ENOSPC) > > return BLK_STS_DEV_RESOURCE; > > return BLK_STS_IOERR; > >
On Thu, Feb 13, 2020 at 8:38 PM Halil Pasic <pasic@linux.ibm.com> wrote: > > Since nobody else is going to restart our hw_queue for us, the > blk_mq_start_stopped_hw_queues() is in virtblk_done() is not sufficient > necessarily sufficient to ensure that the queue will get started again. > In case of global resource outage (-ENOMEM because mapping failure, > because of swiotlb full) our virtqueue may be empty and we can get > stuck with a stopped hw_queue. > > Let us not stop the queue on arbitrary errors, but only on -EONSPC which > indicates a full virtqueue, where the hw_queue is guaranteed to get > started by virtblk_done() before when it makes sense to carry on > submitting requests. Let us also remove a stale comment. The generic solution may be to stop queue only when there is any in-flight request not completed. Checking -ENOMEM may not be enough, given -EIO can be returned from virtqueue_add() too in case of dma map failure. Thanks,
On Tue, 18 Feb 2020 10:21:18 +0800 Ming Lei <tom.leiming@gmail.com> wrote: > On Thu, Feb 13, 2020 at 8:38 PM Halil Pasic <pasic@linux.ibm.com> wrote: > > > > Since nobody else is going to restart our hw_queue for us, the > > blk_mq_start_stopped_hw_queues() is in virtblk_done() is not sufficient > > necessarily sufficient to ensure that the queue will get started again. > > In case of global resource outage (-ENOMEM because mapping failure, > > because of swiotlb full) our virtqueue may be empty and we can get > > stuck with a stopped hw_queue. > > > > Let us not stop the queue on arbitrary errors, but only on -EONSPC which > > indicates a full virtqueue, where the hw_queue is guaranteed to get > > started by virtblk_done() before when it makes sense to carry on > > submitting requests. Let us also remove a stale comment. > > The generic solution may be to stop queue only when there is any > in-flight request > not completed. > I think this is a pretty close to that. The queue is stopped only on ENOSPC, which means virtqueue is full. > Checking -ENOMEM may not be enough, given -EIO can be returned from > virtqueue_add() > too in case of dma map failure. I'm not checking on -ENOMEM. So the queue would not be stopped on EIO. Maybe I'm misunderstanding something In any case, please have another look at the diff, and if your concerns persist please help me understand. Thanks for having a look! Regards, Halil > > Thanks,
On Tue, Feb 18, 2020 at 8:35 PM Halil Pasic <pasic@linux.ibm.com> wrote: > > On Tue, 18 Feb 2020 10:21:18 +0800 > Ming Lei <tom.leiming@gmail.com> wrote: > > > On Thu, Feb 13, 2020 at 8:38 PM Halil Pasic <pasic@linux.ibm.com> wrote: > > > > > > Since nobody else is going to restart our hw_queue for us, the > > > blk_mq_start_stopped_hw_queues() is in virtblk_done() is not sufficient > > > necessarily sufficient to ensure that the queue will get started again. > > > In case of global resource outage (-ENOMEM because mapping failure, > > > because of swiotlb full) our virtqueue may be empty and we can get > > > stuck with a stopped hw_queue. > > > > > > Let us not stop the queue on arbitrary errors, but only on -EONSPC which > > > indicates a full virtqueue, where the hw_queue is guaranteed to get > > > started by virtblk_done() before when it makes sense to carry on > > > submitting requests. Let us also remove a stale comment. > > > > The generic solution may be to stop queue only when there is any > > in-flight request > > not completed. > > > > I think this is a pretty close to that. The queue is stopped only on > ENOSPC, which means virtqueue is full. > > > Checking -ENOMEM may not be enough, given -EIO can be returned from > > virtqueue_add() > > too in case of dma map failure. > > I'm not checking on -ENOMEM. So the queue would not be stopped on EIO. > Maybe I'm misunderstanding something In any case, please have another > look at the diff, and if your concerns persist please help me understand. Looks I misread the patch, and this patch is fine: Reviewed-by: Ming Lei <ming.lei@redhat.com> Thanks, Ming Lei
On Wed, 19 Feb 2020 09:46:56 +0800 Ming Lei <tom.leiming@gmail.com> wrote: > On Tue, Feb 18, 2020 at 8:35 PM Halil Pasic <pasic@linux.ibm.com> wrote: > > > > On Tue, 18 Feb 2020 10:21:18 +0800 > > Ming Lei <tom.leiming@gmail.com> wrote: > > > > > On Thu, Feb 13, 2020 at 8:38 PM Halil Pasic <pasic@linux.ibm.com> wrote: > > > > > > > > Since nobody else is going to restart our hw_queue for us, the > > > > blk_mq_start_stopped_hw_queues() is in virtblk_done() is not sufficient > > > > necessarily sufficient to ensure that the queue will get started again. > > > > In case of global resource outage (-ENOMEM because mapping failure, > > > > because of swiotlb full) our virtqueue may be empty and we can get > > > > stuck with a stopped hw_queue. > > > > > > > > Let us not stop the queue on arbitrary errors, but only on -EONSPC which > > > > indicates a full virtqueue, where the hw_queue is guaranteed to get > > > > started by virtblk_done() before when it makes sense to carry on > > > > submitting requests. Let us also remove a stale comment. > > > > > > The generic solution may be to stop queue only when there is any > > > in-flight request > > > not completed. > > > > > > > I think this is a pretty close to that. The queue is stopped only on > > ENOSPC, which means virtqueue is full. > > > > > Checking -ENOMEM may not be enough, given -EIO can be returned from > > > virtqueue_add() > > > too in case of dma map failure. > > > > I'm not checking on -ENOMEM. So the queue would not be stopped on EIO. > > Maybe I'm misunderstanding something In any case, please have another > > look at the diff, and if your concerns persist please help me understand. > > Looks I misread the patch, and this patch is fine: > > Reviewed-by: Ming Lei <ming.lei@redhat.com> Thank you very much! Regards, Halil > > > Thanks, > Ming Lei
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 54158766334b..adfe43f5ffe4 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -245,10 +245,12 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, err = virtblk_add_req(vblk->vqs[qid].vq, vbr, vbr->sg, num); if (err) { virtqueue_kick(vblk->vqs[qid].vq); - blk_mq_stop_hw_queue(hctx); + /* Don't stop the queue if -ENOMEM: we may have failed to + * bounce the buffer due to global resource outage. + */ + if (err == -ENOSPC) + blk_mq_stop_hw_queue(hctx); spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags); - /* Out of mem doesn't actually happen, since we fall back - * to direct descriptors */ if (err == -ENOMEM || err == -ENOSPC) return BLK_STS_DEV_RESOURCE; return BLK_STS_IOERR;
Since nobody else is going to restart our hw_queue for us, the blk_mq_start_stopped_hw_queues() is in virtblk_done() is not sufficient necessarily sufficient to ensure that the queue will get started again. In case of global resource outage (-ENOMEM because mapping failure, because of swiotlb full) our virtqueue may be empty and we can get stuck with a stopped hw_queue. Let us not stop the queue on arbitrary errors, but only on -EONSPC which indicates a full virtqueue, where the hw_queue is guaranteed to get started by virtblk_done() before when it makes sense to carry on submitting requests. Let us also remove a stale comment. Signed-off-by: Halil Pasic <pasic@linux.ibm.com> Cc: Jens Axboe <axboe@kernel.dk> Fixes: f7728002c1c7 ("virtio_ring: fix return code on DMA mapping fails") --- I'm in doubt with regards to the Fixes tag. The thing is, virtio-blk probably made an assumption on virtqueue_add: the failure is either because the virtqueue is full, or the failure is fatal. In both cases it seems acceptable to stop the queue, although the fatal case is arguable. Since commit f7728002c1c7 it the dma mapping has failed returns -ENOMEM and not -EIO, and thus we have a recoverable failure that ain't virtqueue full. So I lean towards to a fixes tag that references that commit, although it ain't broken. Alternatively one could say 'Fixes: e467cde23818 ("Block driver using virtio.")', if the aforementioned assumption shouldn't have made in the first place. --- drivers/block/virtio_blk.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)