Replace the global part of the lglock with a percpu-rwsem. Since fcl_lock is a spinlock and itself nests under i_lock, which too is a spinlock we cannot acquire sleeping locks at locks_{insert,remove}_global_locks(). We can however wrap all fcl_lock acquisitions with percpu_down_read such that all invocations of locks_{insert,remove}_global_locks() have that read lock held. This allows us to replace the lg_global part of the lglock with the write side of the rwsem. In the absense of writers, percpu_{down,up}_read() are free of atomic instructions. This further avoids the very long preempt-disable regions caused by lglock on larger machines. Cc: der.herr@hofr.at Cc: Al Viro Cc: mingo@redhat.com Cc: torvalds@linux-foundation.org Cc: dave@stgolabs.net Cc: Oleg Nesterov Cc: riel@redhat.com Cc: tj@kernel.org Cc: paulmck@linux.vnet.ibm.com Signed-off-by: Peter Zijlstra (Intel) --- fs/locks.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) --- a/fs/locks.c +++ b/fs/locks.c @@ -164,6 +164,7 @@ int lease_break_time = 45; */ DEFINE_STATIC_LGLOCK(file_lock_lglock); static DEFINE_PER_CPU(struct hlist_head, file_lock_list); +DEFINE_STATIC_PERCPU_RWSEM(file_rwsem); /* * The blocked_hash is used to find POSIX lock loops for deadlock detection. @@ -587,6 +588,8 @@ static int posix_same_owner(struct file_ /* Must be called with the flc_lock held! */ static void locks_insert_global_locks(struct file_lock *fl) { + percpu_rwsem_assert_held(&file_rwsem); + lg_local_lock(&file_lock_lglock); fl->fl_link_cpu = smp_processor_id(); hlist_add_head(&fl->fl_link, this_cpu_ptr(&file_lock_list)); @@ -596,6 +599,8 @@ static void locks_insert_global_locks(st /* Must be called with the flc_lock held! */ static void locks_delete_global_locks(struct file_lock *fl) { + percpu_rwsem_assert_held(&file_rwsem); + /* * Avoid taking lock if already unhashed. This is safe since this check * is done while holding the flc_lock, and new insertions into the list @@ -915,6 +920,7 @@ static int flock_lock_inode(struct inode return -ENOMEM; } + percpu_down_read(&file_rwsem); spin_lock(&ctx->flc_lock); if (request->fl_flags & FL_ACCESS) goto find_conflict; @@ -955,6 +961,7 @@ static int flock_lock_inode(struct inode out: spin_unlock(&ctx->flc_lock); + percpu_up_read(&file_rwsem); if (new_fl) locks_free_lock(new_fl); locks_dispose_list(&dispose); @@ -991,6 +998,7 @@ static int posix_lock_inode(struct inode new_fl2 = locks_alloc_lock(); } + percpu_down_read(&file_rwsem); spin_lock(&ctx->flc_lock); /* * New lock request. Walk all POSIX locks and look for conflicts. If @@ -1162,6 +1170,7 @@ static int posix_lock_inode(struct inode } out: spin_unlock(&ctx->flc_lock); + percpu_up_read(&file_rwsem); /* * Free any unused locks. */ @@ -1436,6 +1445,7 @@ int __break_lease(struct inode *inode, u return error; } + percpu_down_read(&file_rwsem); spin_lock(&ctx->flc_lock); time_out_leases(inode, &dispose); @@ -1487,9 +1497,13 @@ int __break_lease(struct inode *inode, u locks_insert_block(fl, new_fl); trace_break_lease_block(inode, new_fl); spin_unlock(&ctx->flc_lock); + percpu_up_read(&file_rwsem); + locks_dispose_list(&dispose); error = wait_event_interruptible_timeout(new_fl->fl_wait, !new_fl->fl_next, break_time); + + percpu_down_read(&file_rwsem); spin_lock(&ctx->flc_lock); trace_break_lease_unblock(inode, new_fl); locks_delete_block(new_fl); @@ -1506,6 +1520,7 @@ int __break_lease(struct inode *inode, u } out: spin_unlock(&ctx->flc_lock); + percpu_up_read(&file_rwsem); locks_dispose_list(&dispose); locks_free_lock(new_fl); return error; @@ -1660,6 +1675,7 @@ generic_add_lease(struct file *filp, lon return -EINVAL; } + percpu_down_read(&file_rwsem); spin_lock(&ctx->flc_lock); time_out_leases(inode, &dispose); error = check_conflicting_open(dentry, arg, lease->fl_flags); @@ -1730,6 +1746,7 @@ generic_add_lease(struct file *filp, lon lease->fl_lmops->lm_setup(lease, priv); out: spin_unlock(&ctx->flc_lock); + percpu_up_read(&file_rwsem); locks_dispose_list(&dispose); if (is_deleg) inode_unlock(inode); @@ -1752,6 +1769,7 @@ static int generic_delete_lease(struct f return error; } + percpu_down_read(&file_rwsem); spin_lock(&ctx->flc_lock); list_for_each_entry(fl, &ctx->flc_lease, fl_list) { if (fl->fl_file == filp && @@ -1764,6 +1782,7 @@ static int generic_delete_lease(struct f if (victim) error = fl->fl_lmops->lm_change(victim, F_UNLCK, &dispose); spin_unlock(&ctx->flc_lock); + percpu_up_read(&file_rwsem); locks_dispose_list(&dispose); return error; } @@ -2703,6 +2722,7 @@ static void *locks_start(struct seq_file struct locks_iterator *iter = f->private; iter->li_pos = *pos + 1; + percpu_down_write(&file_rwsem); lg_global_lock(&file_lock_lglock); spin_lock(&blocked_lock_lock); return seq_hlist_start_percpu(&file_lock_list, &iter->li_cpu, *pos); @@ -2721,6 +2741,7 @@ static void locks_stop(struct seq_file * { spin_unlock(&blocked_lock_lock); lg_global_unlock(&file_lock_lglock); + percpu_up_write(&file_rwsem); } static const struct seq_operations locks_seq_operations = {