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btrfs: locking: remove the recursion handling code

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Now that we're no longer using recursion, rip out all of the supporting
code.  Follow up patches will clean up the callers of these functions.

The extent_buffer::lock_owner is still retained as it allows safety
checks in btrfs_init_new_buffer for the case that the free space cache
is corrupted and we try to allocate a block that we are currently using
and have locked in the path.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Josef Bacik 2020-11-06 16:27:32 -05:00 committed by David Sterba
parent 2f5239dcb2
commit 4048daedb9
1 changed files with 4 additions and 64 deletions
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68
fs/btrfs/locking.c
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@ -25,43 +25,18 @@
* - reader/reader sharing
* - try-lock semantics for readers and writers
*
* Additionally we need one level nesting recursion, see below. The rwsem
* implementation does opportunistic spinning which reduces number of times the
* locking task needs to sleep.
*
*
* Lock recursion
* --------------
*
* A write operation on a tree might indirectly start a look up on the same
* tree. This can happen when btrfs_cow_block locks the tree and needs to
* lookup free extents.
*
* btrfs_cow_block
* ..
* alloc_tree_block_no_bg_flush
* btrfs_alloc_tree_block
* btrfs_reserve_extent
* ..
* load_free_space_cache
* ..
* btrfs_lookup_file_extent
* btrfs_search_slot
*
* The rwsem implementation does opportunistic spinning which reduces number of
* times the locking task needs to sleep.
*/
/*
* __btrfs_tree_read_lock - lock extent buffer for read
* @eb: the eb to be locked
* @nest: the nesting level to be used for lockdep
* @recurse: if this lock is able to be recursed
* @recurse: unused
*
* This takes the read lock on the extent buffer, using the specified nesting
* level for lockdep purposes.
*
* If you specify recurse = true, then we will allow this to be taken if we
* currently own the lock already. This should only be used in specific
* usecases, and the subsequent unlock will not change the state of the lock.
*/
void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest,
bool recurse)
@ -71,31 +46,7 @@ void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting ne
if (trace_btrfs_tree_read_lock_enabled())
start_ns = ktime_get_ns();
if (unlikely(recurse)) {
/* First see if we can grab the lock outright */
if (down_read_trylock(&eb->lock))
goto out;
/*
* Ok still doesn't necessarily mean we are already holding the
* lock, check the owner.
*/
if (eb->lock_owner != current->pid) {
down_read_nested(&eb->lock, nest);
goto out;
}
/*
* Ok we have actually recursed, but we should only be recursing
* once, so blow up if we're already recursed, otherwise set
* ->lock_recursed and carry on.
*/
BUG_ON(eb->lock_recursed);
eb->lock_recursed = true;
goto out;
}
down_read_nested(&eb->lock, nest);
out:
eb->lock_owner = current->pid;
trace_btrfs_tree_read_lock(eb, start_ns);
}
@ -136,22 +87,11 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb)
}
/*
* Release read lock. If the read lock was recursed then the lock stays in the
* original state that it was before it was recursively locked.
* Release read lock.
*/
void btrfs_tree_read_unlock(struct extent_buffer *eb)
{
trace_btrfs_tree_read_unlock(eb);
/*
* if we're nested, we have the write lock. No new locking
* is needed as long as we are the lock owner.
* The write unlock will do a barrier for us, and the lock_recursed
* field only matters to the lock owner.
*/
if (eb->lock_recursed && current->pid == eb->lock_owner) {
eb->lock_recursed = false;
return;
}
eb->lock_owner = 0;
up_read(&eb->lock);
}