Re: Linux 2.4.30-rc3 md/ext3 problems (ext3 gurus : please check)

[Hifumi Hisashi]

Hi.

At 07:40 05/04/06, Stephen C. Tweedie wrote:
>Sorry, was offline for a week last week; I'll try to look at this more
>closely tomorrow.  Checking the buffer_uptodate() without either a
>refcount or a lock certainly looks unsafe at first glance.
>
>There are lots of ways to pin the bh in that particular bit of the
>code.  The important thing will be to do so without causing leaks if
>we're truly finished with the buffer after this flush.
>

I have measured the bh refcount before the buffer_uptodate() for a few days.
I found out that the bh refcount sometimes reached to 0 .
So, I think following modifications are effective.

diff -Nru 2.4.30-rc3/fs/jbd/commit.c 2.4.30-rc3_patch/fs/jbd/commit.c
--- 2.4.30-rc3/fs/jbd/commit.c	2005-04-06 17:14:47.000000000 +0900
+++ 2.4.30-rc3_patch/fs/jbd/commit.c	2005-04-06 17:18:49.000000000 +0900
@@ -295,6 +295,7 @@
 		struct buffer_head *bh;
 		jh = jh->b_tprev;	/* Wait on the last written */
 		bh = jh2bh(jh);
+		get_bh(bh);
 		if (buffer_locked(bh)) {
 			spin_unlock(&journal_datalist_lock);
 			unlock_journal(journal);
@@ -302,11 +303,14 @@
 			if (unlikely(!buffer_uptodate(bh)))
 				err = -EIO;
 			/* the journal_head may have been removed now */
+			put_bh(bh);
 			lock_journal(journal);
 			goto write_out_data;
 		} else if (buffer_dirty(bh)) {
+			put_bh(bh);
 			goto write_out_data_locked;
 		}
+		put_bh(bh);
 	} while (jh != commit_transaction->t_sync_datalist);
 	goto write_out_data_locked;



>
>> > If some of the write succeeded and some failed, then I believe the
>> > correct behaviour is to return the number of bytes that succeeded.
>> > However this change to the return status (remember the above patch is
>> > a reversal) causes any failure to over-ride any success. This, I
>> > think, is wrong.
>>
>> Yeap, that part also looks wrong.
>
>Certainly it's normal for a short read/write to imply either error or
>EOF, without the error necessarily needing to be returned explicitly.
>I'm not convinced that the Singleunix language actually requires that,
>but it seems the most obvious and consistent behaviour.
>
>--Stephen

When an O_SYNC flag is set , if commit_write() succeed but 
generic_osync_inode() return
error due to I/O failure, write() must fail .

I think that following error handling code is rational in 
do_generic_file_write() .

	if (file->f_flags & O_SYNC)
		err = (status < 0) ? status : written;
	else
		err = written ? written : status;
	out:

	return err;


Thanks. 

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