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Date: Wed, 3 Oct 2012 22:43:27 +0400
From: Dmitry Monakhov <dmonakhov@...nvz.org>
To: linux-ext4@...r.kernel.org
Cc: tytso@....edu, jack@...e.cz, Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: [PATCH] ext4: fix ext4_flush_completed_IO wait semantics
BUG #1) All places where we call ext4_flush_completed_IO are broken
because buffered io and DIO/AIO goes through three stages
1) submitted io,
2) completed io (in i_completed_io_list) conversion pended
3) finished io (conversion done)
And by calling ext4_flush_completed_IO we will flush only
requests which were in (2) stage, which is wrong because:
1) punch_hole and truncate _must_ wait for all outstanding unwritten io
regardless to it's state.
2) fsync and nolock_dio_read should also wait because there is
a time window between end_page_writeback() and ext4_add_complete_io()
As result integrity fsync is broken in case of buffered write
to fallocated region:
fsync blkdev_completion
->filemap_write_and_wait_range
->ext4_end_bio
->end_page_writeback
<-- filemap_write_and_wait_range return
->ext4_flush_completed_IO
sees empty i_completed_io_list but pended
conversion still exist
->ext4_add_complete_io
BUG #2) Race window becomes wider due to 'ext4: completed_io locking cleanup V4'
This patch make following changes:
1) ext4_flush_completed_io() now first try to flush completed io and when
wait for any outstanding unwritten io via ext4_unwritten_wait()
2) Rename function to more appropriate name.
3) Assert that all callers of ext4_flush_unwritten_io should hold i_mutex to
prevent endless wait
Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
---
fs/ext4/ext4.h | 3 ++-
fs/ext4/extents.c | 6 +++---
fs/ext4/file.c | 2 +-
fs/ext4/fsync.c | 2 +-
fs/ext4/indirect.c | 8 +++++---
fs/ext4/page-io.c | 10 ++++++----
6 files changed, 18 insertions(+), 13 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 1be2b44..3ab2539 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1947,7 +1947,7 @@ extern void ext4_htree_free_dir_info(struct dir_private_info *p);
/* fsync.c */
extern int ext4_sync_file(struct file *, loff_t, loff_t, int);
-extern int ext4_flush_completed_IO(struct inode *);
+extern int ext4_flush_unwritten_io(struct inode *);
/* hash.c */
extern int ext4fs_dirhash(const char *name, int len, struct
@@ -2371,6 +2371,7 @@ extern const struct file_operations ext4_dir_operations;
extern const struct inode_operations ext4_file_inode_operations;
extern const struct file_operations ext4_file_operations;
extern loff_t ext4_llseek(struct file *file, loff_t offset, int origin);
+extern void ext4_unwritten_wait(struct inode *inode);
/* namei.c */
extern const struct inode_operations ext4_dir_inode_operations;
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c1fcf48..1c94cca 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4268,7 +4268,7 @@ void ext4_ext_truncate(struct inode *inode)
* finish any pending end_io work so we won't run the risk of
* converting any truncated blocks to initialized later
*/
- ext4_flush_completed_IO(inode);
+ ext4_flush_unwritten_io(inode);
/*
* probably first extent we're gonna free will be last in block
@@ -4847,10 +4847,10 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
/* Wait all existing dio workers, newcomers will block on i_mutex */
ext4_inode_block_unlocked_dio(inode);
- inode_dio_wait(inode);
- err = ext4_flush_completed_IO(inode);
+ err = ext4_flush_unwritten_io(inode);
if (err)
goto out_dio;
+ inode_dio_wait(inode);
credits = ext4_writepage_trans_blocks(inode);
handle = ext4_journal_start(inode, credits);
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 39335bd..ca6f07a 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -55,7 +55,7 @@ static int ext4_release_file(struct inode *inode, struct file *filp)
return 0;
}
-static void ext4_unwritten_wait(struct inode *inode)
+void ext4_unwritten_wait(struct inode *inode)
{
wait_queue_head_t *wq = ext4_ioend_wq(inode);
diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index 4600008..be1d89f 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -138,7 +138,7 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
if (inode->i_sb->s_flags & MS_RDONLY)
goto out;
- ret = ext4_flush_completed_IO(inode);
+ ret = ext4_flush_unwritten_io(inode);
if (ret < 0)
goto out;
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 8d849da..37cd5a4 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -807,9 +807,11 @@ ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb,
retry:
if (rw == READ && ext4_should_dioread_nolock(inode)) {
- if (unlikely(!list_empty(&ei->i_completed_io_list)))
- ext4_flush_completed_IO(inode);
-
+ if (unlikely(!atomic_read(&EXT4_I(inode)->i_unwritten))) {
+ mutex_lock(&inode->i_mutex);
+ ext4_flush_unwritten_io(inode);
+ mutex_unlock(&inode->i_mutex);
+ }
/*
* Nolock dioread optimization may be dynamically disabled
* via ext4_inode_block_unlocked_dio(). Check inode's state
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 5b24c40..1f5df21 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -189,8 +189,6 @@ static int ext4_do_flush_completed_IO(struct inode *inode,
list_add_tail(&io->list, &complete);
}
- /* It is important to update all flags for all end_io in one shot w/o
- * dropping the lock.*/
spin_lock_irqsave(&ei->i_completed_io_lock, flags);
while (!list_empty(&complete)) {
io = list_entry(complete.next, ext4_io_end_t, list);
@@ -228,9 +226,13 @@ static void ext4_end_io_work(struct work_struct *work)
ext4_do_flush_completed_IO(io->inode, io);
}
-int ext4_flush_completed_IO(struct inode *inode)
+int ext4_flush_unwritten_io(struct inode *inode)
{
- return ext4_do_flush_completed_IO(inode, NULL);
+ int ret;
+ WARN_ON_ONCE(!mutex_is_locked(&inode->i_mutex));
+ ret = ext4_do_flush_completed_IO(inode, NULL);
+ ext4_unwritten_wait(inode);
+ return ret;
}
ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags)
--
1.7.7.6
--
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