linux-kernel - Re: [PATCH] mm: workingset: fix NULL ptr dereference

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Message-ID: <20180410024152.GC31282@bombadil.infradead.org>
Date:   Mon, 9 Apr 2018 19:41:52 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Chao Yu <yuchao0@...wei.com>, Jaegeuk Kim <jaegeuk@...nel.org>,
        Christopher Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        Chris Fries <cfries@...gle.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] mm: workingset: fix NULL ptr dereference

On Tue, Apr 10, 2018 at 11:33:39AM +0900, Minchan Kim wrote:
> @@ -522,7 +532,7 @@ EXPORT_SYMBOL(radix_tree_preload);
>   */
>  int radix_tree_maybe_preload(gfp_t gfp_mask)
>  {
> -	if (gfpflags_allow_blocking(gfp_mask))
> +	if (gfpflags_allow_blocking(gfp_mask) && !(gfp_mask & __GFP_ZERO))
>  		return __radix_tree_preload(gfp_mask, RADIX_TREE_PRELOAD_SIZE);
>  	/* Preloading doesn't help anything with this gfp mask, skip it */
>  	preempt_disable();

No, you've completely misunderstood what's going on in this function.