6.14-stable review patch. If anyone has any objections, please let me know.
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From: Max Kellermann max.kellermann@ionos.com
commit bbfe756dc3062c1e934f06e5ba39c239aa953b92 upstream.
If bio_add_folio() fails (because it is full), erofs_fileio_scan_folio() needs to submit the I/O request via erofs_fileio_rq_submit() and allocate a new I/O request with an empty `struct bio`. Then it retries the bio_add_folio() call.
However, at this point, erofs_onlinefolio_split() has already been called which increments `folio->private`; the retry will call erofs_onlinefolio_split() again, but there will never be a matching erofs_onlinefolio_end() call. This leaves the folio locked forever and all waiters will be stuck in folio_wait_bit_common().
This bug has been added by commit ce63cb62d794 ("erofs: support unencoded inodes for fileio"), but was practically unreachable because there was room for 256 folios in the `struct bio` - until commit 9f74ae8c9ac9 ("erofs: shorten bvecs[] for file-backed mounts") which reduced the array capacity to 16 folios.
It was now trivial to trigger the bug by manually invoking readahead from userspace, e.g.:
posix_fadvise(fd, 0, st.st_size, POSIX_FADV_WILLNEED);
This should be fixed by invoking erofs_onlinefolio_split() only after bio_add_folio() has succeeded. This is safe: asynchronous completions invoking erofs_onlinefolio_end() will not unlock the folio because erofs_fileio_scan_folio() is still holding a reference to be released by erofs_onlinefolio_end() at the end.
Fixes: ce63cb62d794 ("erofs: support unencoded inodes for fileio") Fixes: 9f74ae8c9ac9 ("erofs: shorten bvecs[] for file-backed mounts") Cc: stable@vger.kernel.org Signed-off-by: Max Kellermann max.kellermann@ionos.com Reviewed-by: Gao Xiang xiang@kernel.org Tested-by: Hongbo Li lihongbo22@huawei.com Link: https://lore.kernel.org/r/20250428230933.3422273-1-max.kellermann@ionos.com Signed-off-by: Gao Xiang xiang@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/erofs/fileio.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/fs/erofs/fileio.c +++ b/fs/erofs/fileio.c @@ -150,10 +150,10 @@ io_retry: io->rq->bio.bi_iter.bi_sector = io->dev.m_pa >> 9; attached = 0; } - if (!attached++) - erofs_onlinefolio_split(folio); if (!bio_add_folio(&io->rq->bio, folio, len, cur)) goto io_retry; + if (!attached++) + erofs_onlinefolio_split(folio); io->dev.m_pa += len; } cur += len;