If we attempt a direct issue to a SCSI device, and it returns BUSY, then we queue the request up normally. However, the SCSI layer may have already setup SG tables etc for this particular command. If we later merge with this request, then the old tables are no longer valid. Once we issue the IO, we only read/write the original part of the request, not the new state of it. This causes data corruption, and is most often noticed with the file system complaining about the just read data being invalid: [ 235.934465] EXT4-fs error (device sda1): ext4_iget:4831: inode #7142: comm dpkg-query: bad extra_isize 24937 (inode size 256) because most of it is garbage... This doesn't happen from the normal issue path, as we will simply defer the request to the hardware queue dispatch list if we fail. Once it's on the dispatch list, we never merge with it. Fix this from the direct issue path by flagging the request as REQ_NOMERGE so we don't change the size of it before issue. See also: https://bugzilla.kernel.org/show_bug.cgi?id=201685 Fixes: 6ce3dd6eec1 ("blk-mq: issue directly if hw queue isn't busy in case of 'none'") Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> --- diff --git a/block/blk-mq.c b/block/blk-mq.c index 3f91c6e5b17a..d8f518c6ea38 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1715,6 +1715,15 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx, break; case BLK_STS_RESOURCE: case BLK_STS_DEV_RESOURCE: + /* + * If direct dispatch fails, we cannot allow any merging on + * this IO. Drivers (like SCSI) may have set up permanent state + * for this request, like SG tables and mappings, and if we + * merge to it later on then we'll still only do IO to the + * original part. + */ + rq->cmd_flags |= REQ_NOMERGE; + blk_mq_update_dispatch_busy(hctx, true); __blk_mq_requeue_request(rq); break; -- Jens Axboe
