linux-kernel - Re: [PATCHv4 02/17] zram: do not use per-CPU compression streams

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Message-ID: <2ckvrkhhioezkjscvwvzclspikstx2sreglsyie5bi725fypdm@bxxuqtulk3gl>
Date: Sun, 9 Feb 2025 01:41:28 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Yosry Ahmed <yosry.ahmed@...ux.dev>, Kairui Song <ryncsn@...il.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 02/17] zram: do not use per-CPU compression streams

On (25/02/09 01:20), Sergey Senozhatsky wrote:
> So I moved lockdep class keys to per-zram device and per-zsmalloc pool
> to separate the lockdep chains.  Looks like that did the trick.
> 
> 
[..]
> 
> [ 1714.900906] [    T172] Chain exists of:
>                             ptlock_ptr(ptdesc)#2 --> zram-entry->lock --> &zstrm->lock
> 
> [ 1714.903183] [    T172]  Possible unsafe locking scenario:
> 
> [ 1714.904463] [    T172]        CPU0                    CPU1
> [ 1714.905380] [    T172]        ----                    ----
> [ 1714.906293] [    T172]   lock(&zstrm->lock);
> [ 1714.907006] [    T172]                                lock(zram-entry->lock);
> [ 1714.908204] [    T172]                                lock(&zstrm->lock);
> [ 1714.909347] [    T172]   lock(ptlock_ptr(ptdesc)#2);
> [ 1714.910179] [    T172]
>                            *** DEADLOCK ***

Actually, let me look at this more.  Maybe I haven't figured it out yet.