[Devel] [PATCH RHEL7 COMMIT] iomap: report collisions between directio and buffered writes to userspace

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1160.11.1.vz7.172.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.11.1.vz7.172.10
------>
commit 869a1f437939141634637538e3ab5ef4128e767b
Author: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>
Date:   Sat Jan 30 14:43:05 2021 +0300

    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 at oracle.com>
    Reviewed-by: Liu Bo <bo.li.liu at oracle.com>
    
    (cherry-picked from 5a9d929d6e13278df62bd9e3d3ceae8c87ad1eea)
    file_path changed to d_path
    https://jira.sw.ru/browse/PSBM-124609
    Signed-off-by: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>
---
 fs/direct-io.c     | 24 +++++++++++++++++++++++-
 include/linux/fs.h |  1 +
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index f5fd6ff..886989d 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -256,6 +256,27 @@ static void dio_iodone2_helper(struct dio *dio, loff_t offset,
 	}
 }
 
+/*
+ * 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 = d_path(&filp->f_path, 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
@@ -312,7 +333,8 @@ static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret,
 		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);
 	}
 
 	/*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index aee8adf..bc5417f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3316,6 +3316,7 @@ enum {
 };
 
 void dio_end_io(struct bio *bio, int error);
+void dio_warn_stale_pagecache(struct file *filp);
 
 ssize_t __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 	struct block_device *bdev, struct iov_iter *iter, loff_t offset,