Re: [PATCH] fs: xfs: xfs_log: Don't use KM_MAYFAIL at xfs_log_reserve().

[Dave Chinner <david@fromorbit.com>]

On Fri, Aug 02, 2019 at 06:13:12AM +0900, Tetsuo Handa wrote:
> On 2019/08/02 3:50, Luis Chamberlain wrote:
> > That's quite an opaque commit log for what started off as a severe email
> > thread of potential leak of information. As such, can you expand on this
> > commit log considerably to explain the situation a bit better? Your
> > initial thread here provided much clearer evidence of the issue. As-is
> > this commit log tells the reader *nothing* about the potential harm in
> > not applying this patch.
> > 
> > You had mentioned you identified this issue present on at least
> > 4.18 till 5.3-rc1. So, I'm at least inclined to consider this for
> > stable for at least v4.19.
> > 
> > However, what about older kernels? Now that you have identified
> > a fix, were the flag changed in prior commits, is it a regression
> > that perhaps added KM_MAYFAIL at some point?
> 
> I only checked 4.18+ so that RHEL8 will backport this patch. According to
> Brian Foster, commit eb01c9cd87 ("[XFS] Remove the xlog_ticket allocator")
> ( https://git.kernel.org/linus/eb01c9cd87 ) which dates back to April 2008
> added KM_MAYFAIL flag for this allocation
> 
> -	buf = (xfs_caddr_t) kmem_zalloc(PAGE_SIZE, KM_SLEEP);
> +	tic = kmem_zone_zalloc(xfs_log_ticket_zone, KM_SLEEP|KM_MAYFAIL);
> 
> though Dave Chinner thinks that the log ticket rework is irrelevant.
> Do we need to find which commit made this problem visible?

No.

-Dave.
-- 
Dave Chinner
david@fromorbit.com