From: "Huang\, Ying" <ying.huang@intel.com>
To: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
"Hugh Dickins" <hughd@google.com>,
"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
"Minchan Kim" <minchan@kernel.org>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"Tim Chen" <tim.c.chen@linux.intel.com>,
"Mel Gorman" <mgorman@techsingularity.net>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Michal Hocko" <mhocko@suse.com>,
"Andrea Arcangeli" <aarcange@redhat.com>,
"David Rientjes" <rientjes@google.com>,
"Rik van Riel" <riel@redhat.com>, "Jan Kara" <jack@suse.cz>,
"Dave Jiang" <dave.jiang@intel.com>,
"Andrea Parri" <andrea.parri@amarulasolutions.com>
Subject: Re: [PATCH -mm -V7] mm, swap: fix race between swapoff and some swap operations
Date: Tue, 12 Feb 2019 14:40:48 +0800 [thread overview]
Message-ID: <87a7j1ldan.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <20190211190646.j6pdxqirc56inbbe@ca-dmjordan1.us.oracle.com> (Daniel Jordan's message of "Mon, 11 Feb 2019 14:06:46 -0500")
Daniel Jordan <daniel.m.jordan@oracle.com> writes:
> On Mon, Feb 11, 2019 at 04:38:46PM +0800, Huang, Ying wrote:
>> +struct swap_info_struct *get_swap_device(swp_entry_t entry)
>> +{
>> + struct swap_info_struct *si;
>> + unsigned long type, offset;
>> +
>> + if (!entry.val)
>> + goto out;
>
>> + type = swp_type(entry);
>> + si = swap_type_to_swap_info(type);
>
> These lines can be collapsed into swp_swap_info if you want.
Yes. I can use that function to reduce another line from the patch.
Thanks! Will do that.
>> + if (!si)
>> + goto bad_nofile;
>> +
>> + preempt_disable();
>> + if (!(si->flags & SWP_VALID))
>> + goto unlock_out;
>
> After Hugh alluded to barriers, it seems the read of SWP_VALID could be
> reordered with the write in preempt_disable at runtime. Without smp_mb()
> between the two, couldn't this happen, however unlikely a race it is?
>
> CPU0 CPU1
>
> __swap_duplicate()
> get_swap_device()
> // sees SWP_VALID set
> swapoff
> p->flags &= ~SWP_VALID;
> spin_unlock(&p->lock); // pair w/ smp_mb
> ...
> stop_machine(...)
> p->swap_map = NULL;
> preempt_disable()
> read NULL p->swap_map
Andrea has helped to explain this.
Best Regards,
Huang, Ying
next prev parent reply other threads:[~2019-02-12 6:40 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-11 8:38 [PATCH -mm -V7] mm, swap: fix race between swapoff and some swap operations Huang, Ying
2019-02-11 19:06 ` Daniel Jordan
2019-02-12 3:21 ` Andrea Parri
[not found] ` <874l99ld05.fsf@yhuang-dev.intel.com>
2019-02-12 17:58 ` Tim Chen
2019-02-13 3:23 ` Huang, Ying
2019-02-12 20:06 ` Daniel Jordan
2019-02-12 6:40 ` Huang, Ying [this message]
2019-02-12 10:13 ` Andrea Parri
2019-02-14 2:38 ` Andrea Arcangeli
[not found] ` <87k1i2oks6.fsf@yhuang-dev.intel.com>
2019-02-14 21:47 ` Andrea Arcangeli
2019-02-15 7:50 ` Huang, Ying
2019-02-14 14:33 ` Michal Hocko
2019-02-14 20:30 ` Andrew Morton
2019-02-14 21:22 ` Andrea Arcangeli
[not found] ` <871s49bkaz.fsf@yhuang-dev.intel.com>
2019-02-15 13:11 ` Michal Hocko
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