It is trivial to trigger a WARN_ON_ONCE(1) in iomap_dio_actor() by unprivileged users which would taint the kernel, or worse - panic if panic_on_warn or panic_on_taint is set. Hence, just convert it to pr_warn_ratelimited() to let users know their workloads are racing. Thank Dave Chinner for the initial analysis of the racing reproducers.
Signed-off-by: Qian Cai <[email protected]> --- v3: Keep the default case and update the message. v2: Record the path, pid and command as well. fs/iomap/direct-io.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c index c1aafb2ab990..b7f3311569bd 100644 --- a/fs/iomap/direct-io.c +++ b/fs/iomap/direct-io.c @@ -374,6 +374,7 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length, void *data, struct iomap *iomap, struct iomap *srcmap) { struct iomap_dio *dio = data; + char pathname[128], *path; switch (iomap->type) { case IOMAP_HOLE: @@ -388,6 +389,21 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length, return iomap_dio_bio_actor(inode, pos, length, dio, iomap); case IOMAP_INLINE: return iomap_dio_inline_actor(inode, pos, length, dio, iomap); + case IOMAP_DELALLOC: + /* + * DIO is not serialised against mmap() access at all, and so + * if the page_mkwrite occurs between the writeback and the + * iomap_apply() call in the DIO path, then it will see the + * DELALLOC block that the page-mkwrite allocated. + */ + path = file_path(dio->iocb->ki_filp, pathname, + sizeof(pathname)); + if (IS_ERR(path)) + path = "(unknown)"; + + pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %s Comm: %.20s\n", + path, current->comm); + return -EIO; default: WARN_ON_ONCE(1); return -EIO; -- 2.18.4
