From: Qian Cai cai@lca.pw
[ Upstream commit a805c111650cdba6ee880f528abdd03c1af82089 ]
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 cai@lca.pw Reviewed-by: Christoph Hellwig hch@lst.de Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/iomap/direct-io.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c index 7b5f76efef02d..8c98fd92bf665 100644 --- a/fs/iomap/direct-io.c +++ b/fs/iomap/direct-io.c @@ -377,6 +377,16 @@ 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. + */ + pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %pD4 Comm: %.20s\n", + dio->iocb->ki_filp, current->comm); + return -EIO; default: WARN_ON_ONCE(1); return -EIO;