From 5b25f70f4200766355cdabda604e131d2fb6010d Mon Sep 17 00:00:00 2001 From: Arne Jansen Date: Tue, 13 Sep 2011 10:55:48 +0200 Subject: [PATCH] Btrfs: add nested locking mode for paths This patch adds the possibilty to read-lock an extent even if it is already write-locked from the same thread. btrfs_find_all_roots() needs this capability. Signed-off-by: Arne Jansen Signed-off-by: Jan Schmidt --- fs/btrfs/extent_io.c | 1 + fs/btrfs/extent_io.h | 2 ++ fs/btrfs/locking.c | 53 ++++++++++++++++++++++++++++++++++++++++++-- 3 files changed, 54 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index be1bf627a14b..dd8d140eb27b 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -3571,6 +3571,7 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree, atomic_set(&eb->blocking_writers, 0); atomic_set(&eb->spinning_readers, 0); atomic_set(&eb->spinning_writers, 0); + eb->lock_nested = 0; init_waitqueue_head(&eb->write_lock_wq); init_waitqueue_head(&eb->read_lock_wq); diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h index 7604c3001322..bc6a042cb6fc 100644 --- a/fs/btrfs/extent_io.h +++ b/fs/btrfs/extent_io.h @@ -129,6 +129,7 @@ struct extent_buffer { struct list_head leak_list; struct rcu_head rcu_head; atomic_t refs; + pid_t lock_owner; /* count of read lock holders on the extent buffer */ atomic_t write_locks; @@ -137,6 +138,7 @@ struct extent_buffer { atomic_t blocking_readers; atomic_t spinning_readers; atomic_t spinning_writers; + int lock_nested; /* protects write locks */ rwlock_t lock; diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c index d77b67c4b275..5e178d8f7167 100644 --- a/fs/btrfs/locking.c +++ b/fs/btrfs/locking.c @@ -33,6 +33,14 @@ void btrfs_assert_tree_read_locked(struct extent_buffer *eb); */ void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw) { + if (eb->lock_nested) { + read_lock(&eb->lock); + if (eb->lock_nested && current->pid == eb->lock_owner) { + read_unlock(&eb->lock); + return; + } + read_unlock(&eb->lock); + } if (rw == BTRFS_WRITE_LOCK) { if (atomic_read(&eb->blocking_writers) == 0) { WARN_ON(atomic_read(&eb->spinning_writers) != 1); @@ -57,6 +65,14 @@ void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw) */ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw) { + if (eb->lock_nested) { + read_lock(&eb->lock); + if (&eb->lock_nested && current->pid == eb->lock_owner) { + read_unlock(&eb->lock); + return; + } + read_unlock(&eb->lock); + } if (rw == BTRFS_WRITE_LOCK_BLOCKING) { BUG_ON(atomic_read(&eb->blocking_writers) != 1); write_lock(&eb->lock); @@ -81,12 +97,25 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw) void btrfs_tree_read_lock(struct extent_buffer *eb) { again: + read_lock(&eb->lock); + if (atomic_read(&eb->blocking_writers) && + current->pid == eb->lock_owner) { + /* + * This extent is already write-locked by our thread. We allow + * an additional read lock to be added because it's for the same + * thread. btrfs_find_all_roots() depends on this as it may be + * called on a partly (write-)locked tree. + */ + BUG_ON(eb->lock_nested); + eb->lock_nested = 1; + read_unlock(&eb->lock); + return; + } + read_unlock(&eb->lock); wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0); read_lock(&eb->lock); if (atomic_read(&eb->blocking_writers)) { read_unlock(&eb->lock); - wait_event(eb->write_lock_wq, - atomic_read(&eb->blocking_writers) == 0); goto again; } atomic_inc(&eb->read_locks); @@ -129,6 +158,7 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb) } atomic_inc(&eb->write_locks); atomic_inc(&eb->spinning_writers); + eb->lock_owner = current->pid; return 1; } @@ -137,6 +167,15 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb) */ void btrfs_tree_read_unlock(struct extent_buffer *eb) { + if (eb->lock_nested) { + read_lock(&eb->lock); + if (eb->lock_nested && current->pid == eb->lock_owner) { + eb->lock_nested = 0; + read_unlock(&eb->lock); + return; + } + read_unlock(&eb->lock); + } btrfs_assert_tree_read_locked(eb); WARN_ON(atomic_read(&eb->spinning_readers) == 0); atomic_dec(&eb->spinning_readers); @@ -149,6 +188,15 @@ void btrfs_tree_read_unlock(struct extent_buffer *eb) */ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb) { + if (eb->lock_nested) { + read_lock(&eb->lock); + if (eb->lock_nested && current->pid == eb->lock_owner) { + eb->lock_nested = 0; + read_unlock(&eb->lock); + return; + } + read_unlock(&eb->lock); + } btrfs_assert_tree_read_locked(eb); WARN_ON(atomic_read(&eb->blocking_readers) == 0); if (atomic_dec_and_test(&eb->blocking_readers)) @@ -181,6 +229,7 @@ again: WARN_ON(atomic_read(&eb->spinning_writers)); atomic_inc(&eb->spinning_writers); atomic_inc(&eb->write_locks); + eb->lock_owner = current->pid; return 0; } -- 2.20.1