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ext4: never fall back to buffered I/O for atomic direct writes - #1281

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ext4: never fall back to buffered I/O for atomic direct writes#1281
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@blktests-ci-kpd blktests-ci-kpd Bot commented Sep 9, 2026

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Pull request for series with
subject: ext4: never fall back to buffered I/O for atomic direct writes
version: 1
url: https://patchwork.kernel.org/series/1161607/

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Upstream branch: 893e117
series: https://patchwork.kernel.org/series/1161607/
version: 1

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blktests-ci-kpd Bot commented Sep 10, 2026

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Upstream branch: 50d05c7
series: https://patchwork.kernel.org/series/1161607/
version: 1

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blktests-ci-kpd Bot force-pushed the series/1161607=>linus-master branch from cb229f3 to ae7488e Compare September 10, 2026 15:31
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Upstream branch: 5225b8e
series: https://patchwork.kernel.org/series/1161607/
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blktests-ci-kpd Bot force-pushed the series/1161607=>linus-master branch from ae7488e to 992ce45 Compare September 12, 2026 02:28
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blktests-ci-kpd Bot commented Sep 13, 2026

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Upstream branch: 2f0c1cf
series: https://patchwork.kernel.org/series/1161607/
version: 1

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Upstream branch: 2f0c1cf
series: https://patchwork.kernel.org/series/1161607/
version: 1

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Upstream branch: 2f0c1cf
series: https://patchwork.kernel.org/series/1161607/
version: 1

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Upstream branch: 2f0c1cf
series: https://patchwork.kernel.org/series/1161607/
version: 1

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blktests-ci-kpd Bot force-pushed the series/1161607=>linus-master branch from 992ce45 to bf679fd Compare September 13, 2026 09:37
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Upstream branch: 2f0c1cf
series: https://patchwork.kernel.org/series/1161607/
version: 1

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blktests-ci-kpd Bot force-pushed the series/1161607=>linus-master branch from bf679fd to 4fee257 Compare September 13, 2026 22:57
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Upstream branch: 5878583
series: https://patchwork.kernel.org/series/1161607/
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Upstream branch: f49a343
series: https://patchwork.kernel.org/series/1161607/
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Upstream branch: 6812ce4
series: https://patchwork.kernel.org/series/1161607/
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Upstream branch: 72d3fcf
series: https://patchwork.kernel.org/series/1161607/
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Upstream branch: 551c722
series: https://patchwork.kernel.org/series/1161607/
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blktests-ci-kpd Bot force-pushed the series/1161607=>linus-master branch from c2b7d2c to 6616780 Compare October 1, 2026 16:14
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Upstream branch: ce1e022
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Upstream branch: e767a4e
series: https://patchwork.kernel.org/series/1161607/
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Upstream branch: a74306e
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series: https://patchwork.kernel.org/series/1161607/
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blktests-ci-kpd Bot commented Oct 6, 2026

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Upstream branch: 22430ae
series: https://patchwork.kernel.org/series/1161607/
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blktests-ci-kpd Bot force-pushed the series/1161607=>linus-master branch from b1f40a0 to 1b7eb01 Compare October 6, 2026 13:16
@tzussman kernel-patches-daemon
ext4: never fall back to buffered I/O for atomic direct writes
6597f17 
ext4_dio_write_iter() finishes a short direct write through the page
cache. For an atomic write that path only warns and then continues,
which would tear the write.

This came out of a block device fix [1], where an IOCB_ATOMIC direct
write could complete short when only part of the buffer could be
pinned, with the rest going through the buffered fallback. Christoph
Hellwig noted that ext4 has the same fallback and only warns in it [2],
and John Garry agreed it should reject the write instead [3].

In contrast to the block device, nothing reaches the branch on ext4
today: iomap requires the mapping to cover the whole atomic write, a
buffer that can't be pinned in full fails in iomap before the bio is
submitted, and a failed page cache invalidation returns -EAGAIN rather
than reaching the buffered fallback. Exclude atomic writes from the
fallback outright instead of WARN()-ing inside it, so any future bug
yields an error rather than a torn write with a WARN().

Link: https://lore.kernel.org/linux-block/20260828-blkdev-fixes-v2-0-32f3f40cebed@columbia.edu/ [1]
Link: https://lore.kernel.org/linux-block/20260907071217.GD934@lst.de/ [2]
Link: https://lore.kernel.org/linux-block/a7752d1e-8ec1-44d1-a266-c287c315e8ab@oracle.com/ [3]
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
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Upstream branch: 69f80fe
series: https://patchwork.kernel.org/series/1161607/
version: 1

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blktests-ci-kpd Bot force-pushed the series/1161607=>linus-master branch from 1b7eb01 to 6597f17 Compare October 6, 2026 17:30
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