During concurrent append writes to XFS filesystem, zero padding data
may appear in the file after power failure. This happens due to imprecise
disk size updates when handling write completion.
Consider this scenario with concurrent append writes same file:
Thread 1: Thread 2:
------------ -----------
write [A, A+B]
update inode size to A+B
submit I/O [A, A+BS]
write [A+B, A+B+C]
update inode size to A+B+C
<I/O completes, updates disk size to A+B+C>
<power failure>
After reboot, file has zero padding in range [A+B, A+B+C]:
|< Block Size (BS) >|
|DDDDDDDDDDDDDDDD0000000000000000|
^ ^ ^
A A+B A+B+C (EOF)
D = Valid Data
0 = Zero Padding
The issue stems from disk size being set to min(io_offset + io_size,
inode->i_size) at I/O completion. Since io_offset+io_size is block
size granularity, it may exceed the actual valid file data size. In
the case of concurrent append writes, inode->i_size may be larger
than the actual range of valid file data written to disk, leading to
inaccurate disk size updates.
This patch changes the meaning of io_size to represent the size of
valid data in ioend, while the extent size of ioend can be obtained
by rounding up based on block size. It ensures more precise disk
size updates and avoids the zero padding issue. Another benefit is
that it makes the xfs_ioend_is_append() check more accurate, which
can reduce unnecessary end bio callbacks of xfs_end_bio() in certain
scenarios, such as repeated writes at the file tail without extending
the file size.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Long Li <leo.lilong@xxxxxxxxxx>
---
fs/iomap/buffered-io.c | 21 +++++++++++++++------
include/linux/iomap.h | 7 ++++++-
2 files changed, 21 insertions(+), 7 deletions(-)
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index ce73d2a48c1e..a2a75876cda6 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1599,6 +1599,8 @@ EXPORT_SYMBOL_GPL(iomap_finish_ioends);
static bool
iomap_ioend_can_merge(struct iomap_ioend *ioend, struct iomap_ioend *next)
{
+ size_t size = iomap_ioend_extent_size(ioend);
+
if (ioend->io_bio.bi_status != next->io_bio.bi_status)
return false;
if ((ioend->io_flags & IOMAP_F_SHARED) ^
@@ -1607,7 +1609,7 @@ iomap_ioend_can_merge(struct iomap_ioend *ioend, struct iomap_ioend *next)
if ((ioend->io_type == IOMAP_UNWRITTEN) ^
(next->io_type == IOMAP_UNWRITTEN))
return false;
- if (ioend->io_offset + ioend->io_size != next->io_offset)
+ if (ioend->io_offset + size != next->io_offset)
return false;
/*
* Do not merge physically discontiguous ioends. The filesystem
@@ -1619,7 +1621,7 @@ iomap_ioend_can_merge(struct iomap_ioend *ioend, struct iomap_ioend *next)
* submission so does not point to the start sector of the bio at
* completion.
*/
- if (ioend->io_sector + (ioend->io_size >> 9) != next->io_sector)
+ if (ioend->io_sector + (size >> 9) != next->io_sector)
return false;
return true;
}
@@ -1636,7 +1638,7 @@ iomap_ioend_try_merge(struct iomap_ioend *ioend, struct list_head *more_ioends)
if (!iomap_ioend_can_merge(ioend, next))
break;
list_move_tail(&next->io_list, &ioend->io_list);
- ioend->io_size += next->io_size;
+ ioend->io_size = iomap_ioend_extent_size(ioend) + next->io_size;
}
}
EXPORT_SYMBOL_GPL(iomap_ioend_try_merge);
@@ -1736,7 +1738,7 @@ static bool iomap_can_add_to_ioend(struct iomap_writepage_ctx *wpc, loff_t pos)
return false;
if (wpc->iomap.type != wpc->ioend->io_type)
return false;
- if (pos != wpc->ioend->io_offset + wpc->ioend->io_size)
+ if (pos != wpc->ioend->io_offset + iomap_ioend_extent_size(wpc->ioend))
return false;
if (iomap_sector(&wpc->iomap, pos) !=
bio_end_sector(&wpc->ioend->io_bio))
@@ -1768,6 +1770,8 @@ static int iomap_add_to_ioend(struct iomap_writepage_ctx *wpc,
{
struct iomap_folio_state *ifs = folio->private;
size_t poff = offset_in_folio(folio, pos);
+ loff_t isize = i_size_read(inode);
+ struct iomap_ioend *ioend;
int error;
if (!wpc->ioend || !iomap_can_add_to_ioend(wpc, pos)) {
@@ -1778,12 +1782,17 @@ static int iomap_add_to_ioend(struct iomap_writepage_ctx *wpc,
wpc->ioend = iomap_alloc_ioend(wpc, wbc, inode, pos);
}
- if (!bio_add_folio(&wpc->ioend->io_bio, folio, len, poff))
+ ioend = wpc->ioend;
+ if (!bio_add_folio(&ioend->io_bio, folio, len, poff))
goto new_ioend;
if (ifs)
atomic_add(len, &ifs->write_bytes_pending);
- wpc->ioend->io_size += len;
+
+ ioend->io_size = iomap_ioend_extent_size(ioend) + len;
+ if (ioend->io_offset + ioend->io_size > isize)
+ ioend->io_size = isize - ioend->io_offset;
+
wbc_account_cgroup_owner(wbc, folio, len);
return 0;
}
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index f61407e3b121..2984eccfa213 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -330,7 +330,7 @@ struct iomap_ioend {
u16 io_type;
u16 io_flags; /* IOMAP_F_* */
struct inode *io_inode; /* file being written to */
- size_t io_size; /* size of the extent */
+ size_t io_size; /* size of valid data */
loff_t io_offset; /* offset in the file */
sector_t io_sector; /* start sector of ioend */
struct bio io_bio; /* MUST BE LAST! */
@@ -341,6 +341,11 @@ static inline struct iomap_ioend *iomap_ioend_from_bio(struct bio *bio)
return container_of(bio, struct iomap_ioend, io_bio);
}
+static inline size_t iomap_ioend_extent_size(struct iomap_ioend *ioend)
+{
+ return round_up(ioend->io_size, i_blocksize(ioend->io_inode));
+}
+
struct iomap_writeback_ops {
/*
* Required, maps the blocks so that writeback can be performed on
--
2.39.2
