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Date: Tue, 23 Jan 2024 21:18:45 +0100 (CET)
From: Mikulas Patocka <mpatocka@redhat.com>
To: Johannes Thumshirn <johannes.thumshirn@wdc.com>
cc: Damien Le Moal <dlemoal@kernel.org>, Naohiro Aota <naohiro.aota@wdc.com>, 
    Mike Snitzer <snitzer@kernel.org>, dm-devel@lists.linux.dev, 
    Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>, 
    David Sterba <dsterba@suse.com>, Jaegeuk Kim <jaegeuk@kernel.org>, 
    Chao Yu <chao@kernel.org>, Jens Axboe <axboe@kernel.dk>, 
    Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>, 
    Chaitanya Kulkarni <kch@nvidia.com>, linux-fsdevel@vger.kernel.org, 
    linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, 
    linux-f2fs-devel@lists.sourceforge.net, linux-block@vger.kernel.org, 
    linux-nvme@lists.infradead.org, 
    "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: Re: [PATCH 2/5] dm: dm-zoned: pass GFP_KERNEL to blkdev_zone_mgmt
In-Reply-To: <20240123-zonefs_nofs-v1-2-cc0b0308ef25@wdc.com>
Message-ID: <55226421-ce21-f769-94e0-d42c97e55e7d@redhat.com>
References: <20240123-zonefs_nofs-v1-0-cc0b0308ef25@wdc.com> <20240123-zonefs_nofs-v1-2-cc0b0308ef25@wdc.com>
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On Tue, 23 Jan 2024, Johannes Thumshirn wrote:

> The call to blkdev_zone_mgmt() in dm-zoned is only used to perform a
> ZONE_RESET operation when freeing a zone.
> 
> This is not done in the IO path, so we can use GFP_KERNEL here, as it will
> never recurse back into the driver on reclaim.

Hi

This doesn't seem safe to me. There's a possible call chain dmz_handle_bio 
-> dmz_put_chunk_mapping -> dmz_free_zone -> dmz_reset_zone -> 
blkdev_zone_mgmt -> recursion (via GFP_KERNEL) back into the dm-zoned 
target.

Mikulas

> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
>  drivers/md/dm-zoned-metadata.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c
> index fdfe30f7b697..a39734f0cb7d 100644
> --- a/drivers/md/dm-zoned-metadata.c
> +++ b/drivers/md/dm-zoned-metadata.c
> @@ -1658,7 +1658,7 @@ static int dmz_reset_zone(struct dmz_metadata *zmd, struct dm_zone *zone)
>  
>  		ret = blkdev_zone_mgmt(dev->bdev, REQ_OP_ZONE_RESET,
>  				       dmz_start_sect(zmd, zone),
> -				       zmd->zone_nr_sectors, GFP_NOIO);
> +				       zmd->zone_nr_sectors, GFP_KERNEL);
>  		if (ret) {
>  			dmz_dev_err(dev, "Reset zone %u failed %d",
>  				    zone->id, ret);
> 
> -- 
> 2.43.0
> 
>