Fix corruption bug in direct dispatch for blk-mq
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Jeremy Cline
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blk-mq-fix-corruption-with-direct-issue.patch
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blk-mq-fix-corruption-with-direct-issue.patch
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From ffe81d45322cc3cb140f0db080a4727ea284661e Mon Sep 17 00:00:00 2001
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From: Jens Axboe <axboe@kernel.dk>
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Date: Tue, 4 Dec 2018 20:06:48 -0700
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Subject: [PATCH] blk-mq: fix corruption with direct issue
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If we attempt a direct issue to a SCSI device, and it returns BUSY, then
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we queue the request up normally. However, the SCSI layer may have
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already setup SG tables etc for this particular command. If we later
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merge with this request, then the old tables are no longer valid. Once
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we issue the IO, we only read/write the original part of the request,
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not the new state of it.
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This causes data corruption, and is most often noticed with the file
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system complaining about the just read data being invalid:
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[ 235.934465] EXT4-fs error (device sda1): ext4_iget:4831: inode #7142: comm dpkg-query: bad extra_isize 24937 (inode size 256)
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because most of it is garbage...
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This doesn't happen from the normal issue path, as we will simply defer
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the request to the hardware queue dispatch list if we fail. Once it's on
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the dispatch list, we never merge with it.
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Fix this from the direct issue path by flagging the request as
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REQ_NOMERGE so we don't change the size of it before issue.
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See also:
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https://bugzilla.kernel.org/show_bug.cgi?id=201685
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Tested-by: Guenter Roeck <linux@roeck-us.net>
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Fixes: 6ce3dd6eec1 ("blk-mq: issue directly if hw queue isn't busy in case of 'none'")
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Cc: stable@vger.kernel.org
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Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Signed-off-by: Jeremy Cline <jcline@redhat.com>
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---
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block/blk-mq.c | 26 +++++++++++++++++++++++++-
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1 file changed, 25 insertions(+), 1 deletion(-)
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diff --git a/block/blk-mq.c b/block/blk-mq.c
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index 3f91c6e5b17a..3262d83b9e07 100644
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--- a/block/blk-mq.c
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+++ b/block/blk-mq.c
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@@ -1715,6 +1715,15 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
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break;
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case BLK_STS_RESOURCE:
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case BLK_STS_DEV_RESOURCE:
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+ /*
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+ * If direct dispatch fails, we cannot allow any merging on
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+ * this IO. Drivers (like SCSI) may have set up permanent state
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+ * for this request, like SG tables and mappings, and if we
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+ * merge to it later on then we'll still only do IO to the
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+ * original part.
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+ */
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+ rq->cmd_flags |= REQ_NOMERGE;
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+
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blk_mq_update_dispatch_busy(hctx, true);
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__blk_mq_requeue_request(rq);
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break;
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@@ -1727,6 +1736,18 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
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return ret;
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}
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+/*
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+ * Don't allow direct dispatch of anything but regular reads/writes,
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+ * as some of the other commands can potentially share request space
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+ * with data we need for the IO scheduler. If we attempt a direct dispatch
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+ * on those and fail, we can't safely add it to the scheduler afterwards
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+ * without potentially overwriting data that the driver has already written.
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+ */
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+static bool blk_rq_can_direct_dispatch(struct request *rq)
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+{
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+ return req_op(rq) == REQ_OP_READ || req_op(rq) == REQ_OP_WRITE;
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+}
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+
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static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
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struct request *rq,
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blk_qc_t *cookie,
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@@ -1748,7 +1769,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
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goto insert;
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}
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- if (q->elevator && !bypass_insert)
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+ if (!blk_rq_can_direct_dispatch(rq) || (q->elevator && !bypass_insert))
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goto insert;
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if (!blk_mq_get_dispatch_budget(hctx))
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@@ -1810,6 +1831,9 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
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struct request *rq = list_first_entry(list, struct request,
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queuelist);
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+ if (!blk_rq_can_direct_dispatch(rq))
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+ break;
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+
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list_del_init(&rq->queuelist);
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ret = blk_mq_request_issue_directly(rq);
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if (ret != BLK_STS_OK) {
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--
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2.19.2
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@ -609,6 +609,9 @@ Patch504: iio-accel-kxcjk1013-Add-more-hardware-ids.patch
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# rhbz 1645070 patch queued upstream for merging into 4.21
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# rhbz 1645070 patch queued upstream for merging into 4.21
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Patch505: asus-fx503-keyb.patch
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Patch505: asus-fx503-keyb.patch
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# https://bugzilla.kernel.org/show_bug.cgi?id=201685
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Patch506: blk-mq-fix-corruption-with-direct-issue.patch
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# END OF PATCH DEFINITIONS
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# END OF PATCH DEFINITIONS
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%endif
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%endif
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@ -1881,6 +1884,9 @@ fi
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#
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#
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#
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#
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%changelog
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%changelog
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* Wed Dec 05 2018 Jeremy Cline <jeremy@jcline.org>
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- Fix corruption bug in direct dispatch for blk-mq
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* Tue Dec 04 2018 Justin M. Forbes <jforbes@fedoraproject.org> - 4.20.0-0.rc5.git1.1
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* Tue Dec 04 2018 Justin M. Forbes <jforbes@fedoraproject.org> - 4.20.0-0.rc5.git1.1
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- Linux v4.20-rc5-21-g0072a0c14d5b
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- Linux v4.20-rc5-21-g0072a0c14d5b
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- Reenable debugging options.
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- Reenable debugging options.
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