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btrfs: don't fallback to buffered IO for NOWAIT direct IO writes

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Currently, for a direct IO write, if we need to fallback to buffered IO,
either to satisfy the whole write operation or just a part of it, we do
it in the current context even if it's a NOWAIT context. This is not ideal
because we currently don't have support for NOWAIT semantics in the
buffered IO path (we can block for several reasons), so we should instead
return -EAGAIN to the caller, so that it knows it should retry (the whole
operation or what's left of it) in a context where blocking is acceptable.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Filipe Manana 2022-07-04 12:42:04 +01:00 committed by David Sterba
parent 8bfc9b2cf4
commit ac5e666951
1 changed files with 15 additions and 1 deletions
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16
fs/btrfs/file.c
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@ -1971,11 +1971,25 @@ again:
if (is_sync_write) if (is_sync_write)
iocb->ki_flags |= IOCB_DSYNC; iocb->ki_flags |= IOCB_DSYNC;
/* If 'err' is -ENOTBLK then it means we must fallback to buffered IO. */ /*
* If 'err' is -ENOTBLK or we have not written all data, then it means
* we must fallback to buffered IO.
*/
if ((err < 0 && err != -ENOTBLK) || !iov_iter_count(from)) if ((err < 0 && err != -ENOTBLK) || !iov_iter_count(from))
goto out; goto out;
buffered: buffered:
/*
* If we are in a NOWAIT context, then return -EAGAIN to signal the caller
* it must retry the operation in a context where blocking is acceptable,
* since we currently don't have NOWAIT semantics support for buffered IO
* and may block there for many reasons (reserving space for example).
*/
if (iocb->ki_flags & IOCB_NOWAIT) {
err = -EAGAIN;
goto out;
}
pos = iocb->ki_pos; pos = iocb->ki_pos;
written_buffered = btrfs_buffered_write(iocb, from); written_buffered = btrfs_buffered_write(iocb, from);
if (written_buffered < 0) { if (written_buffered < 0) {