linux-kernel - Re: [PATCH] mm/vmscan: fix unsequenced modification and access warning

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Message-ID: <20180322095044.GA23100@dhcp22.suse.cz>
Date:   Thu, 22 Mar 2018 10:50:44 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Nick Desaulniers <nick.desaulniers@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        mgorman@...hsingularity.net, vbabka@...e.cz,
        Minchan Kim <minchan@...nel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        paullawrence@...gle.com
Subject: Re: [PATCH] mm/vmscan: fix unsequenced modification and access
 warning

On Wed 21-03-18 14:37:04, Nick Desaulniers wrote:
> Sorry to dig up an old thread but a coworker was asking about this
> patch. This is essentially the code that landed in commit
> f2f43e566a02a3bdde0a65e6a2e88d707c212a29 "mm/vmscan.c: fix unsequenced
> modification and access warning".
> 
> Is .reclaim_idx still correct in the case of try_to_free_pages()?

Yes, it gets initialized from the given gfp_mask. sc.gfp_mask might be
sllightly different but that doesn't change the reclaim_idx because we
only drop __GFP_{FS,IO} which do not have any zone modification effects.

> It
> looks like reclaim_idx is based on the original gfp_mask in
> __node_reclaim(), but in try_to_free_pages() it looks like it may have
> been based on current_gfp_context()? (The sequencing is kind of
> ambiguous, thus fixed in my patch)
> 
> Was there a bug in the original try_to_free_pages() pre commit
> f2f43e566a0, or is .reclaim_idx supposed to be different between
> try_to_free_pages() and __node_reclaim()?

I do not think there was any real bug.
-- 
Michal Hocko
SUSE Labs