fs/sync.c: sync_file_range(2) may use WB_SYNC_ALL writeback
23d0127096cb ("fs/sync.c: make sync_file_range(2) use WB_SYNC_NONE
writeback") claims that sync_file_range(2) syscall was "created for
userspace to be able to issue background writeout and so waiting for
in-flight IO is undesirable there" and changes the writeback (back) to
WB_SYNC_NONE.
This claim is only partially true. It is true for users that use the flag
SYNC_FILE_RANGE_WRITE by itself, as does PostgreSQL, the user that was the
reason for changing to WB_SYNC_NONE writeback.
However, that claim is not true for users that use that flag combination
SYNC_FILE_RANGE_{WAIT_BEFORE|WRITE|_WAIT_AFTER}. Those users explicitly
requested to wait for in-flight IO as well as to writeback of dirty pages.
Re-brand that flag combination as SYNC_FILE_RANGE_WRITE_AND_WAIT and use
WB_SYNC_ALL writeback to perform the full range sync request.
Link: http://lkml.kernel.org/r/20190409114922.30095-1-amir73il@gmail.com
Link: http://lkml.kernel.org/r/20190419072938.31320-1-amir73il@gmail.com
Fixes: 23d0127096cb ("fs/sync.c: make sync_file_range(2) use WB_SYNC_NONE")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Acked-by: Jan Kara <jack@suse.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/sync.c b/fs/sync.c
index 01e8217..4d1ff01 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -292,8 +292,14 @@ int sync_file_range(struct file *file, loff_t offset, loff_t nbytes,
}
if (flags & SYNC_FILE_RANGE_WRITE) {
+ int sync_mode = WB_SYNC_NONE;
+
+ if ((flags & SYNC_FILE_RANGE_WRITE_AND_WAIT) ==
+ SYNC_FILE_RANGE_WRITE_AND_WAIT)
+ sync_mode = WB_SYNC_ALL;
+
ret = __filemap_fdatawrite_range(mapping, offset, endbyte,
- WB_SYNC_NONE);
+ sync_mode);
if (ret < 0)
goto out;
}
@@ -306,9 +312,9 @@ int sync_file_range(struct file *file, loff_t offset, loff_t nbytes,
}
/*
- * sys_sync_file_range() permits finely controlled syncing over a segment of
+ * ksys_sync_file_range() permits finely controlled syncing over a segment of
* a file in the range offset .. (offset+nbytes-1) inclusive. If nbytes is
- * zero then sys_sync_file_range() will operate from offset out to EOF.
+ * zero then ksys_sync_file_range() will operate from offset out to EOF.
*
* The flag bits are:
*
@@ -325,7 +331,7 @@ int sync_file_range(struct file *file, loff_t offset, loff_t nbytes,
* Useful combinations of the flag bits are:
*
* SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE: ensures that all pages
- * in the range which were dirty on entry to sys_sync_file_range() are placed
+ * in the range which were dirty on entry to ksys_sync_file_range() are placed
* under writeout. This is a start-write-for-data-integrity operation.
*
* SYNC_FILE_RANGE_WRITE: start writeout of all dirty pages in the range which
@@ -337,10 +343,13 @@ int sync_file_range(struct file *file, loff_t offset, loff_t nbytes,
* earlier SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE operation to wait
* for that operation to complete and to return the result.
*
- * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER:
+ * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER
+ * (a.k.a. SYNC_FILE_RANGE_WRITE_AND_WAIT):
* a traditional sync() operation. This is a write-for-data-integrity operation
* which will ensure that all pages in the range which were dirty on entry to
- * sys_sync_file_range() are committed to disk.
+ * ksys_sync_file_range() are written to disk. It should be noted that disk
+ * caches are not flushed by this call, so there are no guarantees here that the
+ * data will be available on disk after a crash.
*
*
* SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will detect any