On 2023/3/27 17:35, Jan Kara wrote:
On Thu 23-03-23 22:18:53, Baokun Li wrote:
On 2023/3/23 19:44, Jan Kara wrote:
---
fs/ext4/ext4.h | 3 ++-
fs/ext4/ext4_jbd2.h | 9 +++++----
fs/ext4/super.c | 14 ++++++++++++++
3 files changed, 21 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 08b29c289da4..f60967fa648f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1703,7 +1703,8 @@ struct ext4_sb_info {
/*
* Barrier between writepages ops and changing any inode's JOURNAL_DATA
- * or EXTENTS flag.
+ * or EXTENTS flag or between changing SHOULD_DIOREAD_NOLOCK flag on
+ * remount and writepages ops.
*/
struct percpu_rw_semaphore s_writepages_rwsem;
struct dax_device *s_daxdev;
diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
index 0c77697d5e90..d82bfcdd56e5 100644
--- a/fs/ext4/ext4_jbd2.h
+++ b/fs/ext4/ext4_jbd2.h
@@ -488,6 +488,9 @@ static inline int ext4_free_data_revoke_credits(struct inode *inode, int blocks)
return blocks + 2*(EXT4_SB(inode->i_sb)->s_cluster_ratio - 1);
}
+/* delalloc is a temporary fix to prevent generic/422 test failures*/
+#define EXT4_MOUNT_SHOULD_DIOREAD_NOLOCK (EXT4_MOUNT_DIOREAD_NOLOCK | \
+ EXT4_MOUNT_DELALLOC)
/*
* This function controls whether or not we should try to go down the
* dioread_nolock code paths, which makes it safe to avoid taking
@@ -499,7 +502,8 @@ static inline int ext4_free_data_revoke_credits(struct inode *inode, int blocks)
*/
static inline int ext4_should_dioread_nolock(struct inode *inode)
{
- if (!test_opt(inode->i_sb, DIOREAD_NOLOCK))
+ if (test_opt(inode->i_sb, SHOULD_DIOREAD_NOLOCK) !=
+ EXT4_MOUNT_SHOULD_DIOREAD_NOLOCK)
return 0;
if (!S_ISREG(inode->i_mode))
return 0;
@@ -507,9 +511,6 @@ static inline int ext4_should_dioread_nolock(struct inode *inode)
return 0;
if (ext4_should_journal_data(inode))
return 0;
- /* temporary fix to prevent generic/422 test failures */
- if (!test_opt(inode->i_sb, DELALLOC))
- return 0;
return 1;
}
Is there a need for this SHOULD_DIOREAD_NOLOCK? When called from writeback
we will be protected by s_writepages_rwsem anyway. When called from other
places, we either decide to do dioread_nolock or don't but the situation
can change at any instant so I don't see how unifying this check would
help. And the new SHOULD_DIOREAD_NOLOCK somewhat obfuscates what's going
on.
We're thinking that the mount-related flags in
ext4_should_dioread_nolock() might be modified, such as DELALLOC being
removed because generic/422 test failures were fixed in some other way,
resulting in some unnecessary locking during remount, or for whatever
reason a mount-related flag was added to ext4_should_dioread_nolock(),
and we didn't make a synchronization change in __ext4_remount() that
would cause the problem to recur. So we added this flag to this function
(instead of in ext4.h), so that when we change the mount option in
ext4_should_dioread_nolock(), we directly change this flag, and we don't
have to consider making synchronization changes in __ext4_remount().
We have checked where this function is called and there are two types of
calls to this function:
1. One category is ext4_do_writepages() and mpage_map_one_extent(), which
are protected by s_writepages_rwsem, the location of the problem;
2. The other type is in ext4_page_mkwrite(),
ext4_convert_inline_data_to_extent(), ext4_write_begin() to determine
whether to get the block using ext4_get_block_unwritten() or
ext4_get_block().
1) If we just started fetching written blocks, it looks like there is no
problem;
2) If we start getting unwritten blocks, when DIOREAD_NOLOCK is cleared
by remount,
we will convert the blocks to written in ext4_map_blocks(). The
data=ordered mode ensures that we don't see stale data.
Yes. So do you agree that EXT4_MOUNT_SHOULD_DIOREAD_NOLOCK is not really
needed?
Honza
Yes, I totally agree!
If we unconditionally grabbed s_writepages_rwsem when remounting,
there would be no mount option synchronization problem, and the flag
would be completely unnecessary.
I will send a patch V2 with the changes suggested by you.
--
With Best Regards,
Baokun Li
.
