On 17/09/2024 17:09, Marek Szyprowski wrote:
Hi Max, On 17.09.2024 00:06, Max Gurtovoy wrote:On 12/09/2024 9:46, Marek Szyprowski wrote:Dear All, On 08.08.2024 00:41, Max Gurtovoy wrote:Set the driver data of the hardware context (hctx) to point directly to the virtio block queue. This cleanup improves code readability and reduces the number of dereferences in the fast path. Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx> Signed-off-by: Max Gurtovoy <mgurtovoy@xxxxxxxxxx> --- drivers/block/virtio_blk.c | 42 ++++++++++++++++++++------------------ 1 file changed, 22 insertions(+), 20 deletions(-)This patch landed in recent linux-next as commit 8d04556131c1 ("virtio_blk: implement init_hctx MQ operation"). In my tests I found that it introduces a regression in system suspend/resume operation. From time to time system crashes during suspend/resume cycle. Reverting this patch on top of next-20240911 fixes this problem.Could you please provide a detailed explanation of the system suspend/resume operation and the specific testing methodology employed?In my tests I just call the 'rtcwake -s10 -mmem' command many times in a loop. I use standard Debian image under QEMU/ARM64. Nothing really special.
I run this test on my bare metal x86 server in a loop with fio in the background.
The test passed.Can you please re-test with the linux/master branch with applying this patch on top ?
The occurrence of a kernel panic from this commit is unexpected, given that it primarily involves pointer reassignment without altering the lifecycle of vblk/vqs. In the virtqueue_add_split function, which pointer is becoming null and causing the issue? A detailed analysis would be helpful. The report indicates that the crash occurs sporadically rather than consistently. is it possible that this is a race condition introduced by a different commit? How can we rule out this possibility?This is the commit pointed by bisecting between v6.11-rc1 and next-20240911. The problem is reproducible, it just need a few calls to the rtcwake command.Prior to applying this commit, what were the test results? Specifically, out of 100 test runs, how many passed successfully?All 100 were successful, see https://pastebin.com/3yETvXK9 (kernel is compiled from 6d17035a7402, which is a parent of $subject in linux-next).After applying this commit, what are the updated test results? Again, out of 100 test runs, how many passed successfully?Usually it freezes or panics after the second try, see https://pastebin.com/u5n9K1Dz (kernel compiled from 8d04556131c1, which is $subject in linux-next).I've even managed to catch a kernel panic log of this problem on QEMU's ARM64 'virt' machine: root@target:~# time rtcwake -s10 -mmem rtcwake: wakeup from "mem" using /dev/rtc0 at Thu Sep 12 07:11:52 2024 Unable to handle kernel NULL pointer dereference at virtual address 0000000000000090 Mem abort info: ESR = 0x0000000096000046 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x06: level 2 translation fault Data abort info: ISV = 0, ISS = 0x00000046, ISS2 = 0x00000000 CM = 0, WnR = 1, TnD = 0, TagAccess = 0 GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0 user pgtable: 4k pages, 48-bit VAs, pgdp=0000000046bbb000 ... Internal error: Oops: 0000000096000046 [#1] PREEMPT SMP Modules linked in: bluetooth ecdh_generic ecc rfkill ipv6 CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0H Not tainted 6.11.0-rc6+ #9024 Hardware name: linux,dummy-virt (DT) Workqueue: kblockd blk_mq_requeue_work pstate: 800000c5 (Nzcv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : virtqueue_add_split+0x458/0x63c lr : virtqueue_add_split+0x1d0/0x63c ... Call trace: virtqueue_add_split+0x458/0x63c virtqueue_add_sgs+0xc4/0xec virtblk_add_req+0x8c/0xf4 virtio_queue_rq+0x6c/0x1bc blk_mq_dispatch_rq_list+0x21c/0x714 __blk_mq_sched_dispatch_requests+0xb4/0x58c blk_mq_sched_dispatch_requests+0x30/0x6c blk_mq_run_hw_queue+0x14c/0x40c blk_mq_run_hw_queues+0x64/0x124 blk_mq_requeue_work+0x188/0x1bc process_one_work+0x20c/0x608 worker_thread+0x238/0x370 kthread+0x124/0x128 ret_from_fork+0x10/0x20 Code: f9404282 79401c21 b9004a81 f94047e1 (f8206841) ---[ end trace 0000000000000000 ]--- note: kworker/0:0H[9] exited with irqs disabled note: kworker/0:0H[9] exited with preempt_count 1diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 2351f411fa46..35a7a586f6f5 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -129,14 +129,6 @@ static inline blk_status_t virtblk_result(u8 status) } } -static inline struct virtio_blk_vq *get_virtio_blk_vq(struct blk_mq_hw_ctx *hctx) -{ - struct virtio_blk *vblk = hctx->queue->queuedata; - struct virtio_blk_vq *vq = &vblk->vqs[hctx->queue_num]; - - return vq; -} - static int virtblk_add_req(struct virtqueue *vq, struct virtblk_req *vbr) { struct scatterlist out_hdr, in_hdr, *sgs[3]; @@ -377,8 +369,7 @@ static void virtblk_done(struct virtqueue *vq) static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx) { - struct virtio_blk *vblk = hctx->queue->queuedata; - struct virtio_blk_vq *vq = &vblk->vqs[hctx->queue_num]; + struct virtio_blk_vq *vq = hctx->driver_data; bool kick; spin_lock_irq(&vq->lock); @@ -428,10 +419,10 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, const struct blk_mq_queue_data *bd) { struct virtio_blk *vblk = hctx->queue->queuedata; + struct virtio_blk_vq *vq = hctx->driver_data; struct request *req = bd->rq; struct virtblk_req *vbr = blk_mq_rq_to_pdu(req); unsigned long flags; - int qid = hctx->queue_num; bool notify = false; blk_status_t status; int err; @@ -440,26 +431,26 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, if (unlikely(status)) return status; - spin_lock_irqsave(&vblk->vqs[qid].lock, flags); - err = virtblk_add_req(vblk->vqs[qid].vq, vbr); + spin_lock_irqsave(&vq->lock, flags); + err = virtblk_add_req(vq->vq, vbr); if (err) { - virtqueue_kick(vblk->vqs[qid].vq); + virtqueue_kick(vq->vq); /* 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); + spin_unlock_irqrestore(&vq->lock, flags); virtblk_unmap_data(req, vbr); return virtblk_fail_to_queue(req, err); } - if (bd->last && virtqueue_kick_prepare(vblk->vqs[qid].vq)) + if (bd->last && virtqueue_kick_prepare(vq->vq)) notify = true; - spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags); + spin_unlock_irqrestore(&vq->lock, flags); if (notify) - virtqueue_notify(vblk->vqs[qid].vq); + virtqueue_notify(vq->vq); return BLK_STS_OK; } @@ -504,7 +495,7 @@ static void virtio_queue_rqs(struct request **rqlist) struct request *requeue_list = NULL; rq_list_for_each_safe(rqlist, req, next) { - struct virtio_blk_vq *vq = get_virtio_blk_vq(req->mq_hctx); + struct virtio_blk_vq *vq = req->mq_hctx->driver_data; bool kick; if (!virtblk_prep_rq_batch(req)) { @@ -1164,6 +1155,16 @@ static const struct attribute_group *virtblk_attr_groups[] = { NULL, }; +static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data, + unsigned int hctx_idx) +{ + struct virtio_blk *vblk = data; + struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx]; + + hctx->driver_data = vq; + return 0; +} + static void virtblk_map_queues(struct blk_mq_tag_set *set) { struct virtio_blk *vblk = set->driver_data; @@ -1205,7 +1206,7 @@ static void virtblk_complete_batch(struct io_comp_batch *iob) static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob) { struct virtio_blk *vblk = hctx->queue->queuedata; - struct virtio_blk_vq *vq = get_virtio_blk_vq(hctx); + struct virtio_blk_vq *vq = hctx->driver_data; struct virtblk_req *vbr; unsigned long flags; unsigned int len; @@ -1236,6 +1237,7 @@ static const struct blk_mq_ops virtio_mq_ops = { .queue_rqs = virtio_queue_rqs, .commit_rqs = virtio_commit_rqs, .complete = virtblk_request_done, + .init_hctx = virtblk_init_hctx, .map_queues = virtblk_map_queues, .poll = virtblk_poll, };Best regardsBest regards
