Re: [PATCH] SMP race in ext2 - metadata corruption.

[Andrea Arcangeli]

On Thu, Apr 26, 2001 at 11:45:47AM -0400, Alexander Viro wrote:
> 	Ext2 does getblk+wait_on_buffer for new metadata blocks before
> filling them with zeroes. While that is enough for single-processor,
> on SMP we have the following race:
> 
> getblk gives us unlocked, non-uptodate bh
> wait_on_buffer() does nothing
> 					read from device locks it and starts IO
> we zero it out.
> 					on-disk data overwrites our zeroes.
> we mark it dirty
> bdflush writes the old data (_not_ zeroes) back to disk.
> 
> Result: crap in metadata block. Proposed fix: lock_buffer()/unlock_buffer()
> around memset()/mark_buffer_uptodate() instead of wait_on_buffer() before
> them.
> 
> Patch against 2.4.4-pre7 follows. Please, apply.

correct. I bet other fs are affected as well btw.

Andrea