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| author | Nikolay Borisov <nborisov@suse.com> | 2020-01-30 13:59:44 +0100 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2020-03-23 17:01:43 +0100 |
| commit | 2992df73268f78ec9281692b9b44ae92f3933b54 (patch) | |
| tree | 317bf92dc9d5546f91945f21d23eb0fd2e656bce /fs/btrfs/locking.h | |
| parent | btrfs: simplify error handling in __btrfs_write_out_cache() (diff) | |
| download | linux-2992df73268f78ec9281692b9b44ae92f3933b54.tar.xz linux-2992df73268f78ec9281692b9b44ae92f3933b54.zip | |
btrfs: Implement DREW lock
A (D)ouble (R)eader (W)riter (E)xclustion lock is a locking primitive
that allows to have multiple readers or multiple writers but not
multiple readers and writers holding it concurrently.
The code is factored out from the existing open-coded locking scheme
used to exclude pending snapshots from nocow writers and vice-versa.
Current implementation actually favors Readers (that is snapshot
creaters) to writers (nocow writers of the filesystem).
The API provides lock/unlock/trylock for reads and writes.
Formal specification for TLA+ provided by Valentin Schneider is at
https://lore.kernel.org/linux-btrfs/2dcaf81c-f0d3-409e-cb29-733d8b3b4cc9@arm.com/
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/locking.h')
| -rw-r--r-- | fs/btrfs/locking.h | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h index 21a285883e89..d715846c10b8 100644 --- a/fs/btrfs/locking.h +++ b/fs/btrfs/locking.h @@ -6,6 +6,9 @@ #ifndef BTRFS_LOCKING_H #define BTRFS_LOCKING_H +#include <linux/atomic.h> +#include <linux/wait.h> +#include <linux/percpu_counter.h> #include "extent_io.h" #define BTRFS_WRITE_LOCK 1 @@ -13,6 +16,8 @@ #define BTRFS_WRITE_LOCK_BLOCKING 3 #define BTRFS_READ_LOCK_BLOCKING 4 +struct btrfs_path; + void btrfs_tree_lock(struct extent_buffer *eb); void btrfs_tree_unlock(struct extent_buffer *eb); @@ -48,4 +53,19 @@ static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw) BUG(); } +struct btrfs_drew_lock { + atomic_t readers; + struct percpu_counter writers; + wait_queue_head_t pending_writers; + wait_queue_head_t pending_readers; +}; + +int btrfs_drew_lock_init(struct btrfs_drew_lock *lock); +void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock); +void btrfs_drew_write_lock(struct btrfs_drew_lock *lock); +bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock); +void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock); +void btrfs_drew_read_lock(struct btrfs_drew_lock *lock); +void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock); + #endif |