From: David Sterba <dsterba@suse.cz>
To: Nikolay Borisov <nborisov@suse.com>
Cc: dsterba@suse.cz, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 06/11] btrfs: document device locking
Date: Mon, 6 Nov 2017 16:09:16 +0100 [thread overview]
Message-ID: <20171106150916.GH28789@twin.jikos.cz> (raw)
In-Reply-To: <5661b2a4-3f0d-281e-6472-66cd48e08eca@suse.com>
On Mon, Nov 06, 2017 at 05:02:21PM +0200, Nikolay Borisov wrote:
> Right, I did a fresh read and indeed the structure now makes sense. I
> have completely missed the nesting though. Maybe you can nest more
> agressively, now every sentence is aligned to the header, perhaps we
> want to have it one level deeper? Or use more than one - at the mutex
> level ? I don't really have a clear-cut answer for you.
How about that:
/*
* Device locking
* ==============
*
* There are several mutexes that protect manipulation of devices and low-level
* structures like chunks but not block groups, extents or files
*
* uuid_mutex (global lock)
* ------------------------
* protects the fs_uuids list that tracks all per-fs fs_devices, resulting from
* the SCAN_DEV ioctl registration or from mount either implicitly (the first
* device) or requested by the device= mount option
*
* the mutex can be very coarse and can cover long-running operations
*
* protects: updates to fs_devices counters like missing devices, rw devices,
* seeding, structure cloning, openning/closing devices at mount/umount time
*
* global::fs_devs - add, remove, updates to the global list
*
* does not protect: manipulation of the fs_devices::devices list!
*
* btrfs_device::name - renames (write side), read is RCU
*
* fs_devices::device_list_mutex (per-fs, with RCU)
* ------------------------------------------------
* protects updates to fs_devices::devices, ie. adding and deleting
*
* simple list traversal with read-only actions can be done with RCU protection
*
* may be used to exclude some operations from running concurrently without any
* modifications to the list (see write_all_supers)
*
* volume_mutex
* ------------
* coarse lock owned by a mounted filesystem; used to exclude some operations
* that cannot run in parallel and affect the higher-level properties of the
* filesystem like: device add/deleting/resize/replace, or balance
*
* balance_mutex
* -------------
* protects balance structures (status, state) and context accessed from
* several places (internally, ioctl)
*
* chunk_mutex
* -----------
* protects chunks, adding or removing during allocation, trim or when a new
* device is added/removed
*
* cleaner_mutex
* -------------
* a big lock that is held by the cleaner thread and prevents running subvolume
* cleaning together with relocation or delayed iputs
*
*
* Lock nesting
* ============
*
* uuid_mutex
* volume_mutex
* device_list_mutex
* chunk_mutex
* balance_mutex
*/
next prev parent reply other threads:[~2017-11-06 15:11 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-31 17:44 [PATCH 00/11] Device fixes and cleanups David Sterba
2017-10-31 17:44 ` [PATCH 01/11] btrfs: add missing device::flush_bio puts David Sterba
2017-11-02 9:41 ` Nikolay Borisov
2017-11-06 13:24 ` David Sterba
2017-11-02 10:40 ` Anand Jain
2017-10-31 17:44 ` [PATCH 02/11] btrfs: rename device free rcu helper to free_device_rcu David Sterba
2017-10-31 17:44 ` [PATCH 03/11] btrfs: introduce free_device helper David Sterba
2017-10-31 17:44 ` [PATCH 04/11] btrfs: use free_device where opencoded David Sterba
2017-11-02 11:25 ` Anand Jain
2017-10-31 17:44 ` [PATCH 05/11] btrfs: simplify exit paths in btrfs_init_new_device David Sterba
2017-11-06 1:53 ` Anand Jain
2017-10-31 17:44 ` [PATCH 06/11] btrfs: document device locking David Sterba
2017-11-02 10:29 ` Nikolay Borisov
2017-11-06 13:51 ` David Sterba
2017-11-06 15:02 ` Nikolay Borisov
2017-11-06 15:09 ` David Sterba [this message]
2017-11-03 11:13 ` Anand Jain
2017-11-06 2:32 ` Anand Jain
2017-11-06 13:40 ` David Sterba
2017-11-06 13:36 ` David Sterba
2017-10-31 17:44 ` [PATCH 07/11] btrfs: dev_alloc_list is not protected by RCU, use normal list_del David Sterba
2017-10-31 17:44 ` [PATCH 08/11] btrfs: simplify btrfs_close_bdev David Sterba
2017-10-31 17:44 ` [PATCH 09/11] btrfs: switch to RCU for device traversal in btrfs_ioctl_dev_info David Sterba
2017-10-31 17:44 ` [PATCH 10/11] btrfs: switch to RCU for device traversal in btrfs_ioctl_fs_info David Sterba
2017-10-31 17:44 ` [PATCH 11/11] btrfs: use non-RCU list traversal in write_all_supers callees David Sterba
2017-11-02 9:49 ` Nikolay Borisov
2017-11-06 13:59 ` David Sterba
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