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authorQu Wenruo <wqu@suse.com>2021-01-28 14:25:08 +0300
committerDavid Sterba <dsterba@suse.com>2021-02-09 00:59:04 +0300
commit2c4d8cb737b805ca8d890e50c23f2b5eca270733 (patch)
treeec578377a20be06c7341cff4ca120b5bc57e56e2 /fs/btrfs/ctree.c
parent0bb3eb3ee8674d5d20ad3c0c0767e18787bbd761 (diff)
downloadlinux-2c4d8cb737b805ca8d890e50c23f2b5eca270733.tar.xz
btrfs: explain page locking and readahead in read_extent_buffer_pages()
In read_extent_buffer_pages(), if we failed to lock the page atomically, we just exit with return value 0. This is counter-intuitive, as normally if we can't lock what we need, we would return something like EAGAIN. But that return hides under (wait == WAIT_NONE) branch, which only gets triggered for readahead. And for readahead, if we failed to lock the page, it means the extent buffer is either being read by other thread, or has been read and is under modification. Either way the eb will or has been cached, thus readahead has no need to wait for it. Add comment on this counter-intuitive behavior. Reported-by: Dan Carpenter <dan.carpenter@oracle.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/ctree.c')
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