Commit 150cce2d authored by David Sterba's avatar David Sterba
Browse files

btrfs: move extent_buffer::lock_owner to debug section 



The lock_owner is used for a rare corruption case and we haven't seen
any reports in years. Move it to the debugging section of eb.  To close
the holes also move log_index so the final layout looks like:

struct extent_buffer {
        u64                        start;                /*     0     8 */
        long unsigned int          len;                  /*     8     8 */
        long unsigned int          bflags;               /*    16     8 */
        struct btrfs_fs_info *     fs_info;              /*    24     8 */
        spinlock_t                 refs_lock;            /*    32     4 */
        atomic_t                   refs;                 /*    36     4 */
        int                        read_mirror;          /*    40     4 */
        s8                         log_index;            /*    44     1 */

        /* XXX 3 bytes hole, try to pack */

        struct callback_head       callback_head __attribute__((__aligned__(8))); /*    48    16 */
        /* --- cacheline 1 boundary (64 bytes) --- */
        struct rw_semaphore        lock;                 /*    64    40 */
        struct page *              pages[16];            /*   104   128 */

        /* size: 232, cachelines: 4, members: 11 */
        /* sum members: 229, holes: 1, sum holes: 3 */
        /* forced alignments: 1, forced holes: 1, sum forced holes: 3 */
        /* last cacheline: 40 bytes */
} __attribute__((__aligned__(8)));

This saves 8 bytes in total and still keeps the lock on a separate cacheline.

Reviewed-by: default avatarQu Wenruo <wqu@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 321f4992

fs/btrfs/extent-tree.c

+23 −9
Original line number Diff line number Diff line
@@ -4803,6 +4803,28 @@ int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans, 
	return ret;

}



#ifdef CONFIG_BTRFS_DEBUG

/*

 * Extra safety check in case the extent tree is corrupted and extent allocator

 * chooses to use a tree block which is already used and locked.

 */

static bool check_eb_lock_owner(const struct extent_buffer *eb)

{

	if (eb->lock_owner == current->pid) {

		btrfs_err_rl(eb->fs_info,

"tree block %llu owner %llu already locked by pid=%d, extent tree corruption detected",

			     eb->start, btrfs_header_owner(eb), current->pid);

		return true;

	}

	return false;

}

#else

static bool check_eb_lock_owner(struct extent_buffer *eb)

{

	return false;

}

#endif



static struct extent_buffer *

btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,

		      u64 bytenr, int level, u64 owner,
@@ -4816,15 +4838,7 @@ btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root, 
	if (IS_ERR(buf))

		return buf;



	/*

	 * Extra safety check in case the extent tree is corrupted and extent

	 * allocator chooses to use a tree block which is already used and

	 * locked.

	 */

	if (buf->lock_owner == current->pid) {

		btrfs_err_rl(fs_info,

"tree block %llu owner %llu already locked by pid=%d, extent tree corruption detected",

			buf->start, btrfs_header_owner(buf), current->pid);

	if (check_eb_lock_owner(buf)) {

		free_extent_buffer(buf);

		return ERR_PTR(-EUCLEAN);

	}

fs/btrfs/extent_io.h

+2 −2
Original line number Diff line number Diff line
@@ -80,16 +80,16 @@ struct extent_buffer { 
	spinlock_t refs_lock;

	atomic_t refs;

	int read_mirror;

	struct rcu_head rcu_head;

	pid_t lock_owner;

	/* >= 0 if eb belongs to a log tree, -1 otherwise */

	s8 log_index;

	struct rcu_head rcu_head;



	struct rw_semaphore lock;



	struct page *pages[INLINE_EXTENT_BUFFER_PAGES];

#ifdef CONFIG_BTRFS_DEBUG

	struct list_head leak_list;

	pid_t lock_owner;

#endif

};

fs/btrfs/locking.c

+12 −3
Original line number Diff line number Diff line
@@ -103,6 +103,15 @@ void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, struct extent_buff 


#endif



#ifdef CONFIG_BTRFS_DEBUG

static void btrfs_set_eb_lock_owner(struct extent_buffer *eb, pid_t owner)

{

	eb->lock_owner = owner;

}

#else

static void btrfs_set_eb_lock_owner(struct extent_buffer *eb, pid_t owner) { }

#endif



/*

 * Extent buffer locking

 * =====================
@@ -165,7 +174,7 @@ int btrfs_try_tree_read_lock(struct extent_buffer *eb) 
int btrfs_try_tree_write_lock(struct extent_buffer *eb)

{

	if (down_write_trylock(&eb->lock)) {

		eb->lock_owner = current->pid;

		btrfs_set_eb_lock_owner(eb, current->pid);

		trace_btrfs_try_tree_write_lock(eb);

		return 1;

	}
@@ -198,7 +207,7 @@ void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest) 
		start_ns = ktime_get_ns();



	down_write_nested(&eb->lock, nest);

	eb->lock_owner = current->pid;

	btrfs_set_eb_lock_owner(eb, current->pid);

	trace_btrfs_tree_lock(eb, start_ns);

}
@@ -213,7 +222,7 @@ void btrfs_tree_lock(struct extent_buffer *eb) 
void btrfs_tree_unlock(struct extent_buffer *eb)

{

	trace_btrfs_tree_unlock(eb);

	eb->lock_owner = 0;

	btrfs_set_eb_lock_owner(eb, 0);

	up_write(&eb->lock);

}