Yes we need that patch. The commit description is misleading, as this
commit actually fixes a bug on data corruption for SCSI devices.
In the latest Ubuntu 4.15 kernel, __blk_mq_try_issue_directly() (in
"block/blk-mq.c") calls blk_mq_sched_insert_request() if
q->mq_ops->queue_rq() returns BLK_STS_RESOURCE, this is not correct and
is prone to data corruption.
The c616cbee97ae has the following change:
@@ -1785,7 +1764,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct
blk_mq_hw_ctx *hctx,
if (bypass_insert)
return BLK_STS_RESOURCE;
- blk_mq_sched_insert_request(rq, false, run_queue, false);
+ blk_mq_request_bypass_insert(rq, run_queue);
return BLK_STS_OK;
}
This change is subtle, now the I/O will not get merged with other
pending I/O if a direct issue has failed. This fixed the data corruption
for SCSI devices. The bug was not introduced by commit ffe81d45322c.
I recommend them pick up all the relevant patches leading to this
commit. If this is difficult we can do a special back ported patch to
change the code in __blk_mq_try_issue_directly() to handle requeue.
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https://bugs.launchpad.net/bugs/1848739
Title:
[linux-azure] Patch to prevent possible data corruption
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