linux-kernel - Re: [PATCH] sbitmap: Use single per-bitmap counting to wake up queued tags

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Date:   Fri, 11 Nov 2022 08:38:51 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Gabriel Krisman Bertazi <krisman@...e.de>
Cc:     Hugh Dickins <hughd@...gle.com>, Keith Busch <kbusch@...nel.org>,
        Jan Kara <jack@...e.cz>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Liu Song <liusong@...ux.alibaba.com>
Subject: Re: [PATCH] sbitmap: Use single per-bitmap counting to wake up queued tags

On Sat, 5 Nov 2022 19:10:55 -0400, Gabriel Krisman Bertazi wrote:
> sbitmap suffers from code complexity, as demonstrated by recent fixes,
> and eventual lost wake ups on nested I/O completion.  The later happens,
> from what I understand, due to the non-atomic nature of the updates to
> wait_cnt, which needs to be subtracted and eventually reset when equal
> to zero.  This two step process can eventually miss an update when a
> nested completion happens to interrupt the CPU in between the wait_cnt
> updates.  This is very hard to fix, as shown by the recent changes to
> this code.
> 
> [...]

Applied, thanks!

[1/1] sbitmap: Use single per-bitmap counting to wake up queued tags
      commit: 4f8126bb2308066b877859e4b5923ffb54143630

Best regards,
-- 
Jens Axboe