Re: [PATCH v2] acct: fix possible deadlock in acct_pin_kill

[Al Viro]

On Thu, Apr 04, 2019 at 07:44:48PM +0100, Al Viro wrote:

> Huh?  sb_writers is taken when we *open* the new file.  Then we replace
> its ->path.mnt with a clone and transfer the write count from the original
> to new one.  And close the old file while we are at it.
> 
> >From sb_writers POV mainline has
> 	sb_start_write(new_sb)	// in open
> 	sb_start_write(new_sb)	// mnt_want_write() on clone
> 	last write to old_sb, then sb_end_write(old_sb) // acct_pin_kill()
> 	sb_end_write(new_sb)	// mnt_drop_write(mnt)
> and you flip the order of the last two lines.
> 
> Could you explain how exactly does your patch help whatever
> problem overlayfs has?

Ow...  Sorry, -ENOCOFFEE...

Let me wake up properly and look at that thing again.