The patch titled
Subject: fs/sync.c: sync_file_range(2) may use WB_SYNC_ALL writeback
has been added to the -mm tree. Its filename is
fs-syncc-sync_file_range2-may-use-wb_sync_all-writeback.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/fs-syncc-sync_file_range2-may-use-wb_sync_all-writeback.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/fs-syncc-sync_file_range2-may-use-wb_sync_all-writeback.patch
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------------------------------------------------------
From: Amir Goldstein <amir73il@xxxxxxxxx>
Subject: 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
the helper filemap_write_and_wait_range(), that uses WB_SYNC_ALL
writeback, to perform the full range sync request.
Link: http://lkml.kernel.org/r/20190409114922.30095-1-amir73il@xxxxxxxxx
Link: http://lkml.kernel.org/r/20190411112152.32151-1-amir73il@xxxxxxxxx
Fixes: 23d0127096cb ("fs/sync.c: make sync_file_range(2) use WB_SYNC_NONE")
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Acked-by: Jan Kara <jack@xxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/sync.c | 25 ++++++++++++++++++-------
include/uapi/linux/fs.h | 3 +++
2 files changed, 21 insertions(+), 7 deletions(-)
--- a/fs/sync.c~fs-syncc-sync_file_range2-may-use-wb_sync_all-writeback
+++ a/fs/sync.c
@@ -18,8 +18,8 @@
#include <linux/backing-dev.h>
#include "internal.h"
-#define VALID_FLAGS (SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE| \
- SYNC_FILE_RANGE_WAIT_AFTER)
+#define VALID_FLAGS (SYNC_FILE_RANGE_WRITE | SYNC_FILE_RANGE_WRITE_AND_WAIT | \
+ SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WAIT_AFTER)
/*
* Do the filesystem syncing work. For simple filesystems
@@ -235,9 +235,9 @@ SYSCALL_DEFINE1(fdatasync, unsigned int,
}
/*
- * 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:
*
@@ -254,7 +254,7 @@ SYSCALL_DEFINE1(fdatasync, unsigned int,
* 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
@@ -266,10 +266,13 @@ SYSCALL_DEFINE1(fdatasync, unsigned int,
* 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
@@ -338,6 +341,14 @@ int ksys_sync_file_range(int fd, loff_t
mapping = f.file->f_mapping;
ret = 0;
+ if ((flags & SYNC_FILE_RANGE_WRITE_AND_WAIT) ==
+ SYNC_FILE_RANGE_WRITE_AND_WAIT) {
+ /* Unlike SYNC_FILE_RANGE_WRITE alone uses WB_SYNC_ALL */
+ ret = filemap_write_and_wait_range(mapping, offset, endbyte);
+ if (ret < 0)
+ goto out_put;
+ }
+
if (flags & SYNC_FILE_RANGE_WAIT_BEFORE) {
ret = file_fdatawait_range(f.file, offset, endbyte);
if (ret < 0)
--- a/include/uapi/linux/fs.h~fs-syncc-sync_file_range2-may-use-wb_sync_all-writeback
+++ a/include/uapi/linux/fs.h
@@ -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:
_
Patches currently in -mm which might be from amir73il@xxxxxxxxx are
fs-syncc-sync_file_range2-may-use-wb_sync_all-writeback.patch
