Messages in this thread |  | | Date | Mon, 3 Feb 2003 02:13:01 +0100 (CET) | From | Mikulas Patocka <> | Subject | Re: 2.0, 2.2, 2.4, 2.5: fsync buffer race |
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On Sun, 2 Feb 2003, Andrew Morton wrote:
> Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz> wrote: > > > > Hi > > > > there's a race condition in filesystem > > > > let's have a two inodes that are placed in the same buffer. > > > > call fsync on inode 1 > > it goes down to ext2_update_inode [update == 1] > > it calls ll_rw_block at the end > > ll_rw_block starts to write buffer > > ext2_update_inode waits on buffer > > > > while the buffer is writing, another process calls fsync on inode 2 > > it goes again to ext2_update_inode > > it calls ll_rw_block > > ll_rw_block sees buffer locked and exits immediatelly > > ext2_update_inode waits for buffer > > the first write finished, ext2_update_inode exits and changes made by > > second proces to inode 2 ARE NOT WRITTEN TO DISK. > > > > hmm, yes. This is a general weakness in the ll_rw_block() interface. It is > not suitable for data-integrity writeouts, as you've pointed out. > > A suitable fix would be do create a new > > void wait_and_rw_block(...) > { > wait_on_buffer(bh); > ll_rw_block(...); > }
It would fail if other CPU submits IO with ll_rw_block after wait_on_buffer but before ll_rw_block. ll_rw_block really needs to be rewritten.
Mikulas
> and go use that in all the appropriate places. > > I shall make that change for 2.5, thanks. >
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