Re: [PATCH] btrfs: convert data_seqcount to seqcount_mutex_t

[David Sterba]

On Wed, Oct 21, 2020 at 01:17:24PM -0700, Davidlohr Bueso wrote:
> By doing so we can associate the sequence counter to the chunk_mutex
> for lockdep purposes (compiled-out otherwise) and also avoid
> explicitly disabling preemption around the write region as it will now
> be done automatically by the seqcount machinery based on the lock type.

Thanks, the enhanced seqlock is new to me and makes sense regarding
lockdep. I've added a comment to mention the mutex association and added
it to misc-next.

[PATCH] btrfs: convert data_seqcount to seqcount_mutex_t

[Davidlohr Bueso]

By doing so we can associate the sequence counter to the chunk_mutex
for lockdep purposes (compiled-out otherwise) and also avoid
explicitly disabling preemption around the write region as it will now
be done automatically by the seqcount machinery based on the lock type.

Signed-off-by: Davidlohr Bueso 
---
 fs/btrfs/volumes.c |  2 +-
 fs/btrfs/volumes.h | 10 --
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 58b9c419a2b6..b6ee92ddc624 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -431,7 +431,7 @@ static struct btrfs_device *__alloc_device(struct 
btrfs_fs_info *fs_info)
 
atomic_set(>reada_in_flight, 0);
atomic_set(>dev_stats_ccnt, 0);
-   btrfs_device_data_ordered_init(dev);
+   btrfs_device_data_ordered_init(dev, fs_info);
INIT_RADIX_TREE(>reada_zones, GFP_NOFS & ~__GFP_DIRECT_RECLAIM);
INIT_RADIX_TREE(>reada_extents, GFP_NOFS & ~__GFP_DIRECT_RECLAIM);
extent_io_tree_init(fs_info, >alloc_state,
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index bf27ac07d315..ff3ec11bb9d2 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -39,10 +39,10 @@ struct btrfs_io_geometry {
 #if BITS_PER_LONG==32 && defined(CONFIG_SMP)
 #include 
 #define __BTRFS_NEED_DEVICE_DATA_ORDERED
-#define btrfs_device_data_ordered_init(device) \
-   seqcount_init(>data_seqcount)
+#define btrfs_device_data_ordered_init(device, info)   
\
+   seqcount_mutex_init(>data_seqcount, >chunk_mutex)
 #else
-#define btrfs_device_data_ordered_init(device) do { } while (0)
+#define btrfs_device_data_ordered_init(device, info) do { } while (0)
 #endif
 
 #define BTRFS_DEV_STATE_WRITEABLE  (0)
@@ -71,7 +71,7 @@ struct btrfs_device {
blk_status_t last_flush_error;
 
 #ifdef __BTRFS_NEED_DEVICE_DATA_ORDERED
-   seqcount_t data_seqcount;
+   seqcount_mutex_t data_seqcount;
 #endif
 
/* the internal btrfs device id */
@@ -162,11 +162,9 @@ btrfs_device_get_##name(const struct btrfs_device *dev)
\
 static inline void \
 btrfs_device_set_##name(struct btrfs_device *dev, u64 size)\
 {  \
-   preempt_disable();  \
write_seqcount_begin(>data_seqcount);  \
dev->name = size;   \
write_seqcount_end(>data_seqcount);\
-   preempt_enable();   \
 }
 #elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION)
 #define BTRFS_DEVICE_GETSET_FUNCS(name)
\
--
2.26.2