Andrew Morton <[email protected]> writes:
> On Tue, 12 Dec 2006 16:18:32 +0300
> Dmitriy Monakhov <[email protected]> wrote:
>
>> >> but according to filemaps locking rules: mm/filemap.c:77
>> >> ..
>> >> * ->i_mutex (generic_file_buffered_write)
>> >> * ->mmap_sem (fault_in_pages_readable->do_page_fault)
>> >> ..
>> >> I'm confused a litle bit, where is the truth?
>> >
>> > xfs_write() calls generic_file_direct_write() without taking i_mutex for
>> > O_DIRECT writes.
>> Yes, but my quastion is about __generic_file_aio_write_nolock().
>> As i understand _nolock sufix means that i_mutex was already locked
>> by caller, am i right ?
>
> Nope. It just means that __generic_file_aio_write_nolock() doesn't take
> the lock. We don't assume or require that the caller took it. For example
> the raw driver calls generic_file_aio_write_nolock() without taking
> i_mutex. Raw isn't relevant to the problem (although ocfs2 might be). But
> we cannot assume that all callers have taken i_mutex, I think.
>
> I guess we can make that a rule (document it, add
> BUG_ON(!mutex_is_locked(..)) if it isn't a blockdev) if needs be. After
> really checking that this matches reality for all callers.
I've checked generic_file_aio_write_nolock() callers for non blockdev.
Only ocfs2 call it explicitly, and do it under i_mutex.
So we need to do:
1) Change wrong comments.
2) Add BUG_ON(!mutex_is_locked(..)) for non blkdev.
3) Invoke vmtruncate only for non blkdev.
Signed-off-by: Dmitriy Monakhov <[email protected]>
-------
diff --git a/mm/filemap.c b/mm/filemap.c
index 7b84dc8..540ef5e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2046,8 +2046,8 @@ generic_file_direct_write(struct kiocb *
/*
* Sync the fs metadata but not the minor inode changes and
* of course not the data as we did direct DMA for the IO.
- * i_mutex is held, which protects generic_osync_inode() from
- * livelocking.
+ * i_mutex may not being held, if so some specific locking
+ * ordering must protect generic_osync_inode() from livelocking.
*/
if (written >= 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
int err = generic_osync_inode(inode, mapping, OSYNC_METADATA);
@@ -2282,6 +2282,17 @@ __generic_file_aio_write_nolock(struct k
written = generic_file_direct_write(iocb, iov, &nr_segs, pos,
ppos, count, ocount);
+ /*
+ * If host is not S_ISBLK generic_file_direct_write() may
+ * have instantiated a few blocks outside i_size files
+ * Trim these off again.
+ */
+ if (unlikely(written < 0) && !S_ISBLK(inode->i_mode)) {
+ loff_t isize = i_size_read(inode);
+ if (pos + count > isize)
+ vmtruncate(inode, isize);
+ }
+
if (written < 0 || written == count)
goto out;
/*
@@ -2344,6 +2355,13 @@ ssize_t generic_file_aio_write_nolock(st
ssize_t ret;
BUG_ON(iocb->ki_pos != pos);
+ /*
+ * generic_file_buffered_write() may be called inside
+ * __generic_file_aio_write_nolock() even in case of
+ * O_DIRECT for non S_ISBLK files. So i_mutex must be held.
+ */
+ if (!S_ISBLK(inode->i_mode))
+ BUG_ON(!mutex_is_locked(&inode->i_mutex));
ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs,
&iocb->ki_pos);
@@ -2386,8 +2404,8 @@ ssize_t generic_file_aio_write(struct ki
EXPORT_SYMBOL(generic_file_aio_write);
/*
- * Called under i_mutex for writes to S_ISREG files. Returns -EIO if something
- * went wrong during pagecache shootdown.
+ * May be called without i_mutex for writes to S_ISREG files.
+ * Returns -EIO if something went wrong during pagecache shootdown.
*/
static ssize_t
generic_file_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
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