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.
Thanks Dave Chinner for the initial analysis of the racing reproducers.
Signed-off-by: Qian Cai <c...@lca.pw>
---
fs/iomap/direct-io.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index c1aafb2ab990..6a6b4bc13269 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -389,7 +389,14 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t
length,
case IOMAP_INLINE:
return iomap_dio_inline_actor(inode, pos, length, dio, iomap);
default:
- WARN_ON_ONCE(1);
+ /*
+ * 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("page_mkwrite() is racing with DIO read
(iomap->type = %u).\n",
+ iomap->type);
return -EIO;
}
}
--
2.18.4
