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add patch to fix issue with large IO requests

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Several people reported IO-related issues since kernel 6.1.6 [0].
Things got better with 6.1.10, but apparently the issues are not fully
resolved (e.g. [1]).

I ran into an issue with PBS backup of a VM with passed-through disks
(error with 6.1.6, hang with 6.1.10+) and found that the issue did not
occur anymore with v6.3-rc1. Bisecting what fixed the issue led to the
commit in this patch. The hope is that it fixes some other issues too.

The commit has a CC-stable tag for 5.15+, but telling from the absence
of user reports, it was much less likely to trigger before 6.1.x (it's
not clear what x is, because of the other issue in 6.1.6). The commit
says it depends on 613b14884b85 ("block: handle bio_split_to_limits()
NULL return") which is already present as a3f1c82e0413 ("block:
handle bio_split_to_limits() NULL return") in the Ubuntu tree.

[0]: https://forum.proxmox.com/threads/119483/post-530365
[1]: https://forum.proxmox.com/threads/119483/post-537991

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
This commit is contained in:
Fiona Ebner 2023-03-07 15:19:44 +01:00 committed by Thomas Lamprecht
parent 8b2b9abefa
commit 3d016e115f
1 changed files with 69 additions and 0 deletions
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69
patches/kernel/0018-block-don-t-allow-multiple-bios-for-IOCB_NOWAIT-issu.patch Normal file
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@ -0,0 +1,69 @@
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Mon, 16 Jan 2023 08:55:53 -0700
Subject: [PATCH] block: don't allow multiple bios for IOCB_NOWAIT issue
If we're doing a large IO request which needs to be split into multiple
bios for issue, then we can run into the same situation as the below
marked commit fixes - parts will complete just fine, one or more parts
will fail to allocate a request. This will result in a partially
completed read or write request, where the caller gets EAGAIN even though
parts of the IO completed just fine.
Do the same for large bios as we do for splits - fail a NOWAIT request
with EAGAIN. This isn't technically fixing an issue in the below marked
patch, but for stable purposes, we should have either none of them or
both.
This depends on: 613b14884b85 ("block: handle bio_split_to_limits() NULL return")
Cc: stable@vger.kernel.org # 5.15+
Fixes: 9cea62b2cbab ("block: don't allow splitting of a REQ_NOWAIT bio")
Link: https://github.com/axboe/liburing/issues/766
Reported-and-tested-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(commit 67d59247d4b52c917e373f05a807027756ab216f upstream)
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
block/fops.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/block/fops.c b/block/fops.c
index b90742595317..e406aa605327 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -221,6 +221,24 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
bio_endio(bio);
break;
}
+ if (iocb->ki_flags & IOCB_NOWAIT) {
+ /*
+ * This is nonblocking IO, and we need to allocate
+ * another bio if we have data left to map. As we
+ * cannot guarantee that one of the sub bios will not
+ * fail getting issued FOR NOWAIT and as error results
+ * are coalesced across all of them, be safe and ask for
+ * a retry of this from blocking context.
+ */
+ if (unlikely(iov_iter_count(iter))) {
+ bio_release_pages(bio, false);
+ bio_clear_flag(bio, BIO_REFFED);
+ bio_put(bio);
+ blk_finish_plug(&plug);
+ return -EAGAIN;
+ }
+ bio->bi_opf |= REQ_NOWAIT;
+ }
if (is_read) {
if (dio->flags & DIO_SHOULD_DIRTY)
@@ -228,9 +246,6 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
} else {
task_io_account_write(bio->bi_iter.bi_size);
}
- if (iocb->ki_flags & IOCB_NOWAIT)
- bio->bi_opf |= REQ_NOWAIT;
-
dio->size += bio->bi_iter.bi_size;
pos += bio->bi_iter.bi_size;