From: David Sterba <dsterba@suse.cz>
To: Anand Jain <anand.jain@oracle.com>
Cc: David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 10/16] btrfs: remove wrong use of volume_mutex from btrfs_dev_replace_start
Date: Mon, 9 Apr 2018 13:53:01 +0200 [thread overview]
Message-ID: <20180409115301.GL8557@twin.jikos.cz> (raw)
In-Reply-To: <14a1aaa2-f079-c3f0-14db-6376f90ee635@oracle.com>
On Mon, Apr 09, 2018 at 04:39:03PM +0800, Anand Jain wrote:
>
>
> On 04/04/2018 02:34 AM, David Sterba wrote:
> > The volume mutex does not protect against anything in this case, the
> > comment about scrub is right but not related to locking and looks
> > confusing. The comment in btrfs_find_device_missing_or_by_path is wrong
> > and confusing too.
> >
> > The device_list_mutex is not held here to protect device lookup, but in
> > this case device replace cannot run in parallel with device removal (due
> > to exclusive op protection), so we don't need further locking here.
>
> Agreed, usage of device_list_mutex and volume_mutex is kind of redundant.
>
> There are unfinished features in btrfs volume, such as device offline
> while it was mounted (patches in the ML).
>
> It's better to replace volume_mutex with device_list_mutex instead of
> removing it, as we might need it in the context mentioned above.
The device_list_mutex will not do anything useful here. It's taken in
contexts where we need to make sure the device list is locked for writes
or we don't want to let the device disappear (superblock write).
As dev-replace requires the device to exist throughout the whole
operation (src_device), the EXCL_OP bit is the correct protection and we
can't hold device_list_mutex throughout the whole
btrfs_dev_replace_start.
> Or it's not a good idea to clean up until all the features are in place
> otherwise we end up adding the locks again at some point.
The lock is redundant and no new code should depend on it. If you're
going to add a more fine grained locking of devices, then we can revisit
what's the best way to do it and I'm quite sure this will not require
re-adding the volume_mutex as it is used now.
next prev parent reply other threads:[~2018-04-09 11:55 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-03 18:34 [PATCH 00/16 v1] Kill fs_info::volume_mutex David Sterba
2018-04-03 18:34 ` [PATCH 01/16] btrfs: squeeze btrfs_dev_replace_continue_on_mount to its caller David Sterba
2018-04-05 9:40 ` Anand Jain
2018-04-03 18:34 ` [PATCH 02/16] btrfs: make success path out of btrfs_init_dev_replace_tgtdev more clear David Sterba
2018-04-05 9:40 ` Anand Jain
2018-04-03 18:34 ` [PATCH 03/16] btrfs: export and rename free_device David Sterba
2018-04-05 9:41 ` Anand Jain
2018-04-03 18:34 ` [PATCH 04/16] btrfs: move btrfs_init_dev_replace_tgtdev to dev-replace.c and make static David Sterba
2018-04-05 9:41 ` Anand Jain
2018-04-03 18:34 ` [PATCH 05/16] btrfs: move volume_mutex to callers of btrfs_rm_device David Sterba
2018-04-05 9:41 ` Anand Jain
2018-04-05 14:28 ` David Sterba
2018-04-03 18:34 ` [PATCH 06/16] btrfs: move clearing of EXCL_OP out of __cancel_balance David Sterba
2018-04-05 9:42 ` Anand Jain
2018-04-05 14:04 ` David Sterba
2018-04-03 18:34 ` [PATCH 07/16] btrfs: add proper safety check before resuming dev-replace David Sterba
2018-04-06 20:06 ` Sasha Levin
2018-04-07 6:42 ` Anand Jain
2018-04-07 10:43 ` Anand Jain
2018-04-09 11:43 ` David Sterba
2018-04-03 18:34 ` [PATCH 08/16] btrfs: add sanity check when resuming balance after mount David Sterba
2018-04-06 20:06 ` Sasha Levin
2018-04-09 7:23 ` Anand Jain
2018-04-16 6:10 ` Anand Jain
2018-04-17 17:38 ` David Sterba
2018-04-03 18:34 ` [PATCH 09/16] btrfs: cleanup helpers that reset balance state David Sterba
2018-04-09 7:43 ` Anand Jain
2018-04-03 18:34 ` [PATCH 10/16] btrfs: remove wrong use of volume_mutex from btrfs_dev_replace_start David Sterba
2018-04-09 8:39 ` Anand Jain
2018-04-09 8:54 ` Nikolay Borisov
2018-04-09 9:31 ` Anand Jain
2018-04-09 11:53 ` David Sterba [this message]
2018-04-09 14:44 ` Anand Jain
2018-04-09 14:55 ` Anand Jain
2018-04-03 18:34 ` [PATCH 11/16] btrfs: kill btrfs_fs_info::volume_mutex David Sterba
2018-04-09 14:52 ` Anand Jain
2018-04-13 5:30 ` Anand Jain
2018-04-13 13:15 ` David Sterba
2018-04-03 18:34 ` [PATCH 12/16] btrfs: track running balance in a simpler way David Sterba
2018-04-03 18:34 ` [PATCH 13/16] btrfs: remove redundant read-only check from btrfs_cancel_balance David Sterba
2018-04-16 9:43 ` Anand Jain
2018-04-17 17:47 ` David Sterba
2018-04-03 18:34 ` [PATCH 14/16] btrfs: drop lock parameter from update_ioctl_balance_args and rename David Sterba
2018-04-03 18:34 ` [PATCH 15/16] btrfs: use mutex in btrfs_resume_balance_async David Sterba
2018-04-03 18:34 ` [PATCH 16/16] btrfs: open code set_balance_control David Sterba
2018-04-09 15:24 ` Anand Jain
2018-04-05 14:31 ` [PATCH 00/16 v1] Kill fs_info::volume_mutex David Sterba
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