iomap: report collisions between directio and buffered writes to userspace

If two programs simultaneously try to write to the same part of a file
via direct IO and buffered IO, there's a chance that the post-diowrite
pagecache invalidation will fail on the dirty page.  When this happens,
the dio write succeeded, which means that the page cache is no longer
coherent with the disk!

Programs are not supposed to mix IO types and this is a clear case of
data corruption, so store an EIO which will be reflected to userspace
during the next fsync.  Replace the WARN_ON with a ratelimited pr_crit
so that the developers have /some/ kind of breadcrumb to track down the
offending program(s) and file(s) involved.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>

1 files changed, 23 insertions, 1 deletions

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 3aafb3343a65..a0ca9e48e993 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -219,6 +219,27 @@ static inline struct page *dio_get_page(struct dio *dio,
 	return dio->pages[sdio->head];
 }
 
+/*
+ * Warn about a page cache invalidation failure during a direct io write.
+ */
+void dio_warn_stale_pagecache(struct file *filp)
+{
+	static DEFINE_RATELIMIT_STATE(_rs, 86400 * HZ, DEFAULT_RATELIMIT_BURST);
+	char pathname[128];
+	struct inode *inode = file_inode(filp);
+	char *path;
+
+	errseq_set(&inode->i_mapping->wb_err, -EIO);
+	if (__ratelimit(&_rs)) {
+		path = file_path(filp, pathname, sizeof(pathname));
+		if (IS_ERR(path))
+			path = "(unknown)";
+		pr_crit("Page cache invalidation failure on direct I/O.  Possible data corruption due to collision with buffered I/O!\n");
+		pr_crit("File: %s PID: %d Comm: %.20s\n", path, current->pid,
+			current->comm);
+	}
+}
+
 /**
  * dio_complete() - called when all DIO BIO I/O has been completed
  * @offset: the byte offset in the file of the completed operation
@@ -290,7 +311,8 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, unsigned int flags)
 		err = invalidate_inode_pages2_range(dio->inode->i_mapping,
 					offset >> PAGE_SHIFT,
 					(offset + ret - 1) >> PAGE_SHIFT);
-		WARN_ON_ONCE(err);
+		if (err)
+			dio_warn_stale_pagecache(dio->iocb->ki_filp);
 	}
 
 	if (!(dio->flags & DIO_SKIP_DIO_COUNT))