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vdev_disk: fix alignment check when buffer has non-zero starting offset 

If a linear buffer spans multiple pages, and the first page has a
non-zero starting offset, the checker would not include the offset, and
so would think there was an alignment gap at the end of the first page,
rather than at the start.

That is, for a 16K buffer spread across five pages with an initial 512B
offset:

    [.XXXXXXX][XXXXXXXX][XXXXXXXX][XXXXXXXX][XXXXXXX.]

It would be interpreted as:

    [XXXXXXX.][XXXXXXXX]...

And be rejected as misaligned.

Since it's already a linear ABD, the "linearising" copy would just reuse
the buffer as-is, and the second check would failing, tripping the
VERIFY in vdev_disk_io_rw().

This commit fixes all this by including the offset in the check for
end-of-page alignment.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
This commit is contained in:
Rob Norris 2024-04-10 13:14:13 +10:00 committed by Rob Norris
parent 912aec726f
commit 52f60c29d4
2 changed files with 2 additions and 2 deletions
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2
module/os/linux/zfs/vdev_disk.c
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@ -882,7 +882,7 @@ vdev_disk_check_pages_cb(struct page *page, size_t off, size_t len, void *priv)
* Note if we're taking less than a full block, so we can check it * Note if we're taking less than a full block, so we can check it
* above on the next call. * above on the next call.
*/ */
s->end = len & s->bmask; s->end = (off+len) & s->bmask;
/* All blocks after the first must start on a block size boundary. */ /* All blocks after the first must start on a block size boundary. */
if (s->npages != 0 && (off & s->bmask) != 0) if (s->npages != 0 && (off & s->bmask) != 0)

2
tests/zfs-tests/tests/functional/vdev_disk/page_alignment.c
View File

@ -61,7 +61,7 @@ vdev_disk_check_pages_cb(struct page *page, size_t off, size_t len, void *priv)
* Note if we're taking less than a full block, so we can check it * Note if we're taking less than a full block, so we can check it
* above on the next call. * above on the next call.
*/ */
s->end = len & s->bmask; s->end = (off+len) & s->bmask;
/* All blocks after the first must start on a block size boundary. */ /* All blocks after the first must start on a block size boundary. */
if (s->npages != 0 && (off & s->bmask) != 0) if (s->npages != 0 && (off & s->bmask) != 0)