From: Anand Jain <anand.jain@oracle.com>
To: David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 4/6] btrfs: use RCU in btrfs_show_devname for device list traversal
Date: Wed, 28 Mar 2018 04:09:13 +0800 [thread overview]
Message-ID: <789a6571-e79c-5cda-1b90-57d5de8322c6@oracle.com> (raw)
In-Reply-To: <7c574ffc98700bda85d92ffc7b9ad49b65017e9d.1522176187.git.dsterba@suse.com>
On 03/28/2018 02:48 AM, David Sterba wrote:
> The show_devname callback is used to print device name in
> /proc/self/mounts, we need to traverse the device list consistently and
> read the name that's copied to a seq buffer so we don't need further
> locking.
>
> If the first device is being deleted at the same time, the RCU will
> allow us to read the device name, though it will become stale right
> after the RCU protection ends. This is unavoidable and the user can
> expect that the device will disappear from the filesystem's list at some
> point.
>
> The device_list_mutex was pretty heavy as it is used eg. for writing
> superblock and a few other IO related contexts. This can stall any
> application that reads the proc file for no reason.
>
> Signed-off-by: David Sterba <dsterba@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
next prev parent reply other threads:[~2018-03-27 20:12 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-27 18:48 [PATCH 0/6] Btrfs lockdep and locking cleanups David Sterba
2018-03-27 18:48 ` [PATCH 1/6] btrfs: use lockdep_assert_held for spinlocks David Sterba
2018-03-27 18:48 ` [PATCH 2/6] btrfs: use lockdep_assert_held for mutexes David Sterba
2018-03-27 18:48 ` [PATCH 3/6] btrfs: update barrier in should_cow_block David Sterba
2018-03-27 18:48 ` [PATCH 4/6] btrfs: use RCU in btrfs_show_devname for device list traversal David Sterba
2018-03-27 20:09 ` Anand Jain [this message]
2018-03-27 18:48 ` [PATCH 5/6] btrfs: remove stale comments about fs_mutex David Sterba
2018-03-27 18:48 ` [PATCH 6/6] btrfs: split dev-replace locking helpers for read and write David Sterba
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