Messages in this thread Patch in this message | | | Subject | Re: [patch] fix race in __block_prepare_write (again) | From | Nick Piggin <> | Date | Thu, 21 Apr 2005 17:20:57 +1000 |
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On Thu, 2005-04-21 at 08:10 +0100, Anton Altaparmakov wrote: > And one more thing... > > On Thu, 2005-04-21 at 08:01 +0100, Anton Altaparmakov wrote: > > On Thu, 21 Apr 2005, Nick Piggin wrote: > > > ... I somehow didn't send it to Andrew last time. > > > > > > Fix a race where __block_prepare_write can leak out an in-flight > > > read against a bh if get_block returns an error. This can lead to > > > the page becoming unlocked while the buffer is locked and the read > > > still in flight. __mpage_writepage BUGs on this condition. > > [snip] > > > --- linux-2.6.orig/fs/buffer.c 2005-04-21 11:55:17.549614278 > > +1000 > > > +++ linux-2.6/fs/buffer.c 2005-04-21 15:55:41.483826075 +1000 > > > @@ -1988,6 +1988,7 @@ > > > *wait_bh++=bh; > > > } > > > } > > > +out: > > > /* > > > * If we issued read requests - let them complete. > > > */ > > > @@ -1996,8 +1997,9 @@ > > > if (!buffer_uptodate(*wait_bh)) > > > return -EIO; > > This return is now wrong after your patch. It should be "err = -EIO;" > otherwise you do not zero newly allocated blocks and thus risk exposing > stale data on buffer i/o errors. >
Hmm yeah I should have been more careful. But isn't that another bug? I mean, wasn't that wrong *before* my patch as well?
It was, right? Because not only might it return without having waited for all in-flight buffers, but it also didn't zero the blocks on errors?
Fix a race where __block_prepare_write can leak out an in-flight read against a bh if get_block returns an error. This can lead to the page becoming unlocked while the buffer is locked and the read still in flight. __mpage_writepage BUGs on this condition.
BUG sighted on a 2-way Itanium2 system with 16K PAGE_SIZE running
fsstress -v -d $DIR/tmp -n 1000 -p 1000 -l 2
where $DIR is a new ext2 filesystem with 4K blocks that is quite small (causing get_block to fail often with -ENOSPC).
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Index: linux-2.6/fs/buffer.c =================================================================== --- linux-2.6.orig/fs/buffer.c 2005-04-21 11:55:17.549614278 +1000 +++ linux-2.6/fs/buffer.c 2005-04-21 17:20:06.149176996 +1000 @@ -1952,7 +1952,7 @@ if (!buffer_mapped(bh)) { err = get_block(inode, block, bh, 1); if (err) - goto out; + break; if (buffer_new(bh)) { clear_buffer_new(bh); unmap_underlying_metadata(bh->b_bdev, @@ -1994,10 +1994,12 @@ while(wait_bh > wait) { wait_on_buffer(*--wait_bh); if (!buffer_uptodate(*wait_bh)) - return -EIO; + err = -EIO; } - return 0; -out: + if (!err) + return err; + + /* Error case: */ /* * Zero out any newly allocated blocks to avoid exposing stale * data. If BH_New is set, we know that the block was newly | |