Re: [PATCH] zram: Fix __zram_bvec_{read,write}() locking order

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To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH] zram: Fix __zram_bvec_{read,write}() locking order
From: Minchan Kim <minchan@xxxxxxxxxx>
Date: Mon, 19 Oct 2020 07:08:30 -0700
Cc: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>, Linux List Kernel Mailing <linux-kernel@xxxxxxxxxxxxxxx>, linux-block@xxxxxxxxxxxxxxx, Mike Galbraith <umgwanakikbuti@xxxxxxxxx>, ngupta@xxxxxxxxxx, sergey.senozhatsky.work@xxxxxxxxx, bigeasy@xxxxxxxxxxxxx, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
In-reply-to: <20201019101353.GJ2628@hirez.programming.kicks-ass.net>
References: <CABXGCsOL0pW0Ghh-w5d12P75ve6FS9Rgmzm6DvsYbJY-jMTCdg@mail.gmail.com> <20201016124009.GQ2611@hirez.programming.kicks-ass.net> <20201016153324.GA1976566@google.com> <20201019101353.GJ2628@hirez.programming.kicks-ass.net>

On Mon, Oct 19, 2020 at 12:13:53PM +0200, Peter Zijlstra wrote:
> 
> Mikhail reported a lockdep spat detailing how __zram_bvec_read() and
> __zram_bvec_write() use zstrm->lock and zspage->lock in opposite order.
> 
> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>

Thanks for the fix.

References:
- swapon/913 is trying to acquire lock at zcomp_stream_get+0x5/0x90 [zram] but task is already holding lock at zs_map_object+0x7a/0x2e0
  - From: Mikhail Gavrilov
- Re: swapon/913 is trying to acquire lock at zcomp_stream_get+0x5/0x90 [zram] but task is already holding lock at zs_map_object+0x7a/0x2e0
  - From: Peter Zijlstra
- Re: swapon/913 is trying to acquire lock at zcomp_stream_get+0x5/0x90 [zram] but task is already holding lock at zs_map_object+0x7a/0x2e0
  - From: Minchan Kim
- [PATCH] zram: Fix __zram_bvec_{read,write}() locking order
  - From: Peter Zijlstra

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