Commit bd76eca1 authored by Boqun Feng's avatar Boqun Feng Committed by Peter Zijlstra
Browse files

lockdep: Reduce the size of lock_list::distance 



lock_list::distance is always not greater than MAX_LOCK_DEPTH (which
is 48 right now), so a u16 will fit. This patch reduces the size of
lock_list::distance to save space, so that we can introduce other fields
to help detect recursive read lock deadlocks without increasing the size
of lock_list structure.

Suggested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarBoqun Feng <boqun.feng@gmail.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-6-boqun.feng@gmail.com
parent d563bc6e

include/linux/lockdep.h

+1 −1
Original line number Diff line number Diff line
@@ -54,7 +54,7 @@ struct lock_list { 
	struct lock_class		*class;

	struct lock_class		*links_to;

	const struct lock_trace		*trace;

	int				distance;

	u16				distance;



	/*

	 * The parent field is used to implement breadth-first search, and the

kernel/locking/lockdep.c

+3 −3
Original line number Diff line number Diff line
@@ -1320,7 +1320,7 @@ static struct lock_list *alloc_list_entry(void) 
 */

static int add_lock_to_list(struct lock_class *this,

			    struct lock_class *links_to, struct list_head *head,

			    unsigned long ip, int distance,

			    unsigned long ip, u16 distance,

			    const struct lock_trace *trace)

{

	struct lock_list *entry;
@@ -2489,7 +2489,7 @@ check_deadlock(struct task_struct *curr, struct held_lock *next) 
 */

static int

check_prev_add(struct task_struct *curr, struct held_lock *prev,

	       struct held_lock *next, int distance,

	       struct held_lock *next, u16 distance,

	       struct lock_trace **const trace)

{

	struct lock_list *entry;
@@ -2622,7 +2622,7 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next) 
		goto out_bug;



	for (;;) {

		int distance = curr->lockdep_depth - depth + 1;

		u16 distance = curr->lockdep_depth - depth + 1;

		hlock = curr->held_locks + depth - 1;



		/*

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