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io_uring can complete an O_DIRECT read with -EAGAIN on kernels without
commit b08e02045002 ("io_uring/rw: don't gate retry on completion
context"), which was merged for Linux 6.14. This happens on XFS for a
read that spans several extents when a concurrent allocating write
holds the inode lock: the bios for the first extents are already in
flight when mapping a later extent fails with -EAGAIN, iomap completes
the request from a workqueue, and io_uring does not retry it outside
the submitting task. virtio-blk then reports VIRTIO_BLK_S_IOERR to the
guest for data that is intact.
Reissue a read or write that completes with -EAGAIN or -EINTR once,
with IOSQE_ASYNC so that io-wq runs it in blocking mode, where it
cannot fail this way again. QEMU resubmits both errors as well.
Signed-off-by: doge <me@crackerben.com>
rbradford
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Oct 2, 2026
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Thank you but this needs some very careful review
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On our XFS hosts (Linux 6.12), guests logged read errors under concurrent writes:
For each of them the VMM logged:
The data on disk was intact. On the host, each failed request was an
iomap_dio_completetrace event with error -11 in a kworker, followed by anio_uring_completeevent with result -11. Kernels with b08e02045002 (6.14) retry such requests in io_uring.Tested with two new unit tests, the first of which fails on main. They skip on kernels before 6.4, where pipes do not support RWF_NOWAIT. In a Linux guest on an XFS host, 4 threads wrote random 4 KiB blocks with O_DIRECT into a fallocated 32 GiB file while 4 threads read the disk range under it in 1 MiB O_DIRECT reads, for 5 minutes: on main 1,036,069 of 3,714,530 reads failed with EIO, with this change none of 3,168,618 did.