Re: fs: NULL deref in atime_needs_update
From: Al Viro
Date: Mon Feb 29 2016 - 11:20:06 EST
On Mon, Feb 29, 2016 at 04:54:54PM +0100, Dmitry Vyukov wrote:
> Regardless of whether reordering is wrong or not, do we see how it can
> fix the WARNINGs/oopses? Because it does seem to. I've tried to revert
> just this part:
> - *inode = d_backing_inode(dentry);
> negative = d_is_negative(dentry);
> + *inode = d_backing_inode(dentry);
> And got:
> [ 976.609688] WARNING: CPU: 0 PID: 12126 at fs/namei.c:1587
> [ 976.626768] WARNING: CPU: 0 PID: 12126 at fs/namei.c:3123
> in 15 minutes.
dentry going from negative to positive lookup_fast()
fetch NULL ->d_inode
store non-NULL ->d_inode
store new ->d_flags
fetch new ->d_flags
bump ->d_seq by 2
Change the order of fetches and you'll get rid of that scenario.
> In particular, applying this on top the previous patch will be
> inconclusive, because I already don't see the warnings.
Apply it with that reordering reversed, please.