linux-kernel - Re: [PATCH 2/3] block: fix locking for struct block

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Message-ID: <73653f9e-2d39-48fb-9842-3a1851fb5bed@suse.de>
Date:   Mon, 24 Aug 2020 09:36:38 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>
Cc:     Justin Sanders <justin@...aid.com>,
        Josef Bacik <josef@...icpanda.com>,
        Xianting Tian <xianting_tian@....com>,
        linux-block@...r.kernel.org, dm-devel@...hat.com,
        Stefan Haberland <sth@...ux.ibm.com>,
        Jan Hoeppner <hoeppner@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, nbd@...er.debian.org,
        linux-nvme@...ts.infradead.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 2/3] block: fix locking for struct block_device size
 updates

On 8/23/20 11:10 AM, Christoph Hellwig wrote:
> Two different callers use two different mutexes for updating the
> block device size, which obviously doesn't help to actually protect
> against concurrent updates from the different callers.  In addition
> one of the locks, bd_mutex is rather prone to deadlocks with other
> parts of the block stack that use it for high level synchronization.
> 
> Switch to using a new spinlock protecting just the size updates, as
> that is all we need, and make sure everyone does the update through
> the proper helper.
> 
> This fixes a bug reported with the nvme revalidating disks during a
> hot removal operation, which can currently deadlock on bd_mutex.
> 
> Reported-by: Xianting Tian <xianting_tian@....com>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  block/partitions/core.c         |  4 ++--
>  drivers/block/aoe/aoecmd.c      |  4 +---
>  drivers/md/dm.c                 | 15 ++-------------
>  drivers/s390/block/dasd_ioctl.c |  9 ++-------
>  fs/block_dev.c                  | 25 ++++++++++++++-----------
>  include/linux/blk_types.h       |  1 +
>  6 files changed, 22 insertions(+), 36 deletions(-)
> Reviewed-by: Hannes Reinecke <hare@...e.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@...e.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer