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From: Minchan Kim <minchan@kernel.org>
To: Vinayak Menon <vinmenon@codeaurora.org>
Cc: linux-mm@kvack.org
Subject: Re: [PATCH] mm: fix the race between swapin_readahead and SWP_SYNCHRONOUS_IO path
Date: Thu, 12 Sep 2019 10:14:00 -0700	[thread overview]
Message-ID: <20190912171400.GA119788@google.com> (raw)
In-Reply-To: <c7fbc609-0bb0-bffd-8b1f-c2588c89bfd2@codeaurora.org>

Hi Vinayak,

On Wed, Sep 11, 2019 at 03:37:23PM +0530, Vinayak Menon wrote:

< snip >

> >> Can swapcache check be done like below, before taking the SWP_SYNCHRONOUS_IO path, as an alternative ?
> > With your approach, what prevent below scenario?
> >
> > A                                                       B
> >
> >                                             do_swap_page
> >                                             SWP_SYNCHRONOUS_IO && __swap_count == 1
> 
> 
> As shrink_page_list is picking the page from LRU and B is trying to read from swap simultaneously, I assume someone had read
> 
> the page from swap prior to B, when its swap_count was say 2 (for it to be reclaimed by shrink_page_list now)

It could happen after B saw __swap_count == 1. Think about forking new process.
In that case, swap_count is 2 and the forked process will access the page(it
ends up freeing zram slot but the page would be swap cache. However, B process
doesn't know it).


  reply	other threads:[~2019-09-12 17:14 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-30 12:43 [PATCH] mm: fix the race between swapin_readahead and SWP_SYNCHRONOUS_IO path Vinayak Menon
2019-09-02 13:21 ` Michal Hocko
2019-09-03  6:13   ` Vinayak Menon
2019-09-03 11:41     ` Michal Hocko
2019-09-03 12:17       ` Vinayak Menon
2019-09-09  4:05         ` Vinayak Menon
2019-09-09 11:23           ` Michal Hocko
2019-09-09 23:26 ` Minchan Kim
2019-09-10  8:22   ` Vinayak Menon
2019-09-10 17:51     ` Minchan Kim
2019-09-11 10:07       ` Vinayak Menon
2019-09-12 17:14         ` Minchan Kim [this message]
2019-09-13  9:05           ` Vinayak Menon
2019-09-16 20:05             ` Minchan Kim
2019-09-17  5:38               ` Vinayak Menon
2019-09-18  1:12                 ` Minchan Kim

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