linux-kernel - Re: [PATCH AUTOSEL 4.19 071/219] btrfs: Check for missing device before bio submission in btrfs_map

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Message-ID: <20191122113337.GB3001@suse.cz>
Date:   Fri, 22 Nov 2019 12:33:37 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Nikolay Borisov <nborisov@...e.com>,
        Josef Bacik <josef@...icpanda.com>,
        Anand Jain <anand.jain@...cle.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 4.19 071/219] btrfs: Check for missing device
 before bio submission in btrfs_map_bio

On Fri, Nov 22, 2019 at 12:46:43AM -0500, Sasha Levin wrote:
> From: Nikolay Borisov <nborisov@...e.com>
> 
> [ Upstream commit fc8a168aa9ab1680c2bd52bf9db7c994e0f2524f ]
> 
> Before btrfs_map_bio submits all stripe bios it does a number of checks
> to ensure the device for every stripe is present. However, it doesn't do
> a DEV_STATE_MISSING check, instead this is relegated to the lower level
> btrfs_schedule_bio (in the async submission case, sync submission
> doesn't check DEV_STATE_MISSING at all). Additionally
> btrfs_schedule_bios does the duplicate device->bdev check which has
> already been performed in btrfs_map_bio.
> 
> This patch moves the DEV_STATE_MISSING check in btrfs_map_bio and
> removes the duplicate device->bdev check. Doing so ensures that no bio
> cloning/submission happens for both async/sync requests in the face of
> missing device. This makes the async io submission path slightly shorter
> in terms of instruction count. No functional changes.
                                 ^^^^^^^^^^^^^^^^^^^^^

This should be a strong indication that the patch is not suitable for
autosel/stable, please remove it. Thanks.