Commit c553ea4f authored by Amir Goldstein's avatar Amir Goldstein Committed by Linus Torvalds
Browse files

fs/sync.c: sync_file_range(2) may use WB_SYNC_ALL writeback 

23d01270 ("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: 23d01270 ("fs/sync.c: make sync_file_range(2) use WB_SYNC_NONE")
Signed-off-by: default avatarAmir Goldstein <amir73il@gmail.com>
Acked-by: default avatarJan Kara <jack@suse.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 53269057

fs/sync.c

+15 −6
Original line number Diff line number Diff line
@@ -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 @@ out: 
}



/*

 * 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 @@ out: 
 * 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 @@ out: 
 * 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

include/uapi/linux/fs.h

+3 −0
Original line number Diff line number Diff line
@@ -320,6 +320,9 @@ struct fscrypt_key { 
#define SYNC_FILE_RANGE_WAIT_BEFORE	1

#define SYNC_FILE_RANGE_WRITE		2

#define SYNC_FILE_RANGE_WAIT_AFTER	4

#define SYNC_FILE_RANGE_WRITE_AND_WAIT	(SYNC_FILE_RANGE_WRITE | \

					 SYNC_FILE_RANGE_WAIT_BEFORE | \

					 SYNC_FILE_RANGE_WAIT_AFTER)



/*

 * Flags for preadv2/pwritev2:

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