From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Joey Pabalinas <joeypabalinas@gmail.com>
Subject: Re: [PATCH v3 1/7] zram: fix lockdep warning of free block handling
Date: Thu, 29 Nov 2018 11:43:34 +0900 [thread overview]
Message-ID: <20181129024334.GD6379@jagdpanzerIV> (raw)
In-Reply-To: <20181127055429.251614-2-minchan@kernel.org>
On (11/27/18 14:54), Minchan Kim wrote:
> With writeback feature, zram_slot_free_notify could be called
> in softirq context by end_swap_bio_read. However, bitmap_lock
> is not aware of that so lockdep yell out. Thanks.
>
> get_entry_bdev
> spin_lock(bitmap->lock);
> irq
> softirq
> end_swap_bio_read
> zram_slot_free_notify
> zram_slot_lock <-- deadlock prone
> zram_free_page
> put_entry_bdev
> spin_lock(bitmap->lock); <-- deadlock prone
>
> With akpm's suggestion(i.e. bitmap operation is already atomic),
> we could remove bitmap lock. It might fail to find a empty slot
> if serious contention happens. However, it's not severe problem
> because huge page writeback has already possiblity to fail if there
> is severe memory pressure. Worst case is just keeping
> the incompressible in memory, not storage.
>
> The other problem is zram_slot_lock in zram_slot_slot_free_notify.
> To make it safe is this patch introduces zram_slot_trylock where
> zram_slot_free_notify uses it. Although it's rare to be contented,
> this patch adds new debug stat "miss_free" to keep monitoring
> how often it happens.
>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
-ss
next prev parent reply other threads:[~2018-11-29 2:43 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-27 5:54 [PATCH v3 0/7] zram idle page writeback Minchan Kim
2018-11-27 5:54 ` [PATCH v3 1/7] zram: fix lockdep warning of free block handling Minchan Kim
2018-11-29 2:43 ` Sergey Senozhatsky [this message]
2018-11-27 5:54 ` [PATCH v3 2/7] zram: fix double free backing device Minchan Kim
2018-11-29 2:32 ` Sergey Senozhatsky
2018-11-27 5:54 ` [PATCH v3 3/7] zram: refactoring flags and writeback stuff Minchan Kim
2018-11-27 5:54 ` [PATCH v3 4/7] zram: introduce ZRAM_IDLE flag Minchan Kim
2018-11-29 2:29 ` Sergey Senozhatsky
2018-11-27 5:54 ` [PATCH v3 5/7] zram: support idle/huge page writeback Minchan Kim
2018-11-28 23:35 ` Andrew Morton
2018-11-29 1:36 ` Minchan Kim
2018-11-27 5:54 ` [PATCH v3 6/7] zram: add bd_stat statistics Minchan Kim
2018-11-27 5:54 ` [PATCH v3 7/7] zram: writeback throttle Minchan Kim
2018-11-28 23:41 ` Andrew Morton
2018-11-29 1:55 ` Minchan Kim
2018-11-29 2:23 ` Sergey Senozhatsky
2018-12-02 23:18 ` Minchan Kim
2018-12-03 2:30 ` Sergey Senozhatsky
2018-12-03 2:41 ` Minchan Kim
2018-12-03 2:45 ` Sergey Senozhatsky
2018-11-30 4:36 ` [PATCH v3 0/7] zram idle page writeback Sergey Senozhatsky
2018-12-02 23:20 ` Minchan Kim
2018-12-02 23:28 ` Joey Pabalinas
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