From: Qian Cai <cai@lca.pw>
To: Matthew Wilcox <willy@infradead.org>
Cc: akpm@linux-foundation.org, elver@google.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm/vmscan: fix data races at kswapd_classzone_idx
Date: Wed, 26 Feb 2020 08:49:30 -0500 [thread overview]
Message-ID: <1582724970.7365.121.camel@lca.pw> (raw)
In-Reply-To: <20200226040612.GW24185@bombadil.infradead.org>
On Tue, 2020-02-25 at 20:06 -0800, Matthew Wilcox wrote:
> On Tue, Feb 25, 2020 at 10:58:27PM -0500, Qian Cai wrote:
> > pgdat->kswapd_classzone_idx could be accessed concurrently in
> > wakeup_kswapd(). Plain writes and reads without any lock protection
> > result in data races. Fix them by adding a pair of READ|WRITE_ONCE() as
> > well as saving a branch (compilers might well optimize the original code
> > in an unintentional way anyway). While at it, also take care of
> > pgdat->kswapd_order and non-kswapd threads in allow_direct_reclaim().
>
> I don't understand why the usages of kswapd_classzone_idx in kswapd() and
> kswapd_try_to_sleep() don't need changing too? kswapd_classzone_idx()
> looks safe to me, but I'm prone to missing stupid things that compilers
> are allowed to do.
Right, I did capture the race this time. I'll post a v3.
[ 924.803628][ T6299] BUG: KCSAN: data-race in kswapd / wakeup_kswapd
[ 924.809949][ T6299]
[ 924.812170][ T6299] write to 0xffff90973ffff2dc of 4 bytes by task 820 on cpu
6:
[ 924.819630][ T6299] kswapd+0x27c/0x8d0
[ 924.823509][ T6299] kthread+0x1e0/0x200
[ 924.827471][ T6299] ret_from_fork+0x27/0x50
[ 924.831774][ T6299]
[ 924.833987][ T6299] read to 0xffff90973ffff2dc of 4 bytes by task 6299 on cpu
0:
[ 924.841442][ T6299] wakeup_kswapd+0xf3/0x450
[ 924.845838][ T6299] wake_all_kswapds+0x59/0xc0
[ 924.850409][ T6299] __alloc_pages_slowpath+0xdcc/0x1290
[ 924.855769][ T6299] __alloc_pages_nodemask+0x3bb/0x450
[ 924.861040][ T6299] alloc_pages_vma+0x8a/0x2c0
[ 924.865612][ T6299] do_anonymous_page+0x170/0x700
[ 924.870443][ T6299] __handle_mm_fault+0xc9f/0xd00
[ 924.875276][ T6299] handle_mm_fault+0xfc/0x2f0
[ 924.879849][ T6299] do_page_fault+0x263/0x6f9
[ 924.884334][ T6299] page_fault+0x34/0x40
prev parent reply other threads:[~2020-02-26 13:49 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 3:58 [PATCH v2] mm/vmscan: fix data races at kswapd_classzone_idx Qian Cai
2020-02-26 4:06 ` Matthew Wilcox
2020-02-26 11:50 ` Qian Cai
2020-02-26 13:49 ` Qian Cai [this message]
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