linux-kernel - Re: [PATCH] xfs: use GFP_NOFS argument in radix_tree

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150323053715.GK5170@taesoo.org>
Date:	Mon, 23 Mar 2015 01:37:15 -0400
From:	Taesoo Kim <taesoo@...ech.edu>
To:	Dave Chinner <david@...morbit.com>
Cc:	Sanidhya Kashyap <sanidhya.gatech@...il.com>, xfs@....sgi.com,
	linux-kernel@...r.kernel.org, changwoo@...ech.edu,
	sanidhya@...ech.edu, blee@...ech.edu, csong84@...ech.edu
Subject: Re: [PATCH] xfs: use GFP_NOFS argument in radix_tree_preload

Hi Dave,

Thank you for letting us know. Since we are not an expert of XFS (nor
want to be), we really want to let you guys know it's potential bug
that you might miss (we are helping you!). And that's why Sanidhya
asked (rather than sending a patch) at the first place.

I agree that the comment is misleading and not correct, but probably
encouraging a student who spend times to clean up your mistake
might be better way to influence him rather than shouting :)

Taesoo

On 03/23/15 at 04:24pm, Dave Chinner wrote:
> On Mon, Mar 23, 2015 at 01:06:23AM -0400, Sanidhya Kashyap wrote:
> > From: Byoungyoung Lee <blee@...ech.edu>
> > 
> > Following the convention of other file systems, GFP_NOFS
> > should be used as an argument for radix_tree_preload() instead
> > of GFP_KERNEL.
> 
> "convention of other filesystems" is not a reason for changing from
> GFP_KERNEL to GFP_NOFS. There are rules for when GFP_NOFS needs to
> be used, and so we only need to change the code if one of those
> rules are triggered. i.e. inside a transaction, holding a lock that
> memory reclaim might require to make progress (e.g. ip->i_ilock,
> buffer locks, etc). The context in which the allocation is made will
> tell you whether GFP_KERNEL is safe or not.
> 
> So while the change probably needs to be made, it needs to be made
> for the right reasons. I haven't looked at the code, but I have
> a pretty good idea of the context the allocation is being made
> under. I'd suggest documenting the call path down to
> xfs_mru_cache_insert(), because that will tell you exactly what
> context the allocaiton is being made in and hence tell everyone else
> the real reason we need to make this change...
> 
> Call me picky, pendantic and/or annoying, but if you are looking at
> validating/correcting allocation flags then you need to understand
> the rules and context in which the allocation is being made...
> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@...morbit.com
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/