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lockdep: Support deadlock detection for recursive read locks in check_noncircular()

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Currently, lockdep only has limit support for deadlock detection for
recursive read locks.

This patch support deadlock detection for recursive read locks. The
basic idea is:

We are about to add dependency B -> A in to the dependency graph, we use
check_noncircular() to find whether we have a strong dependency path
A -> .. -> B so that we have a strong dependency circle (a closed strong
dependency path):

	 A -> .. -> B -> A

, which doesn't have two adjacent dependencies as -(*R)-> L -(S*)->.

Since A -> .. -> B is already a strong dependency path, so if either
B -> A is -(E*)-> or A -> .. -> B is -(*N)->, the circle A -> .. -> B ->
A is strong, otherwise not. So we introduce a new match function
hlock_conflict() to replace the class_equal() for the deadlock check in
check_noncircular().

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-10-boqun.feng@gmail.com
This commit is contained in:
Boqun Feng 2020-08-07 15:42:28 +08:00 committed by Peter Zijlstra
parent 61775ed243
commit 9de0c9bbce
1 changed files with 35 additions and 8 deletions
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43
kernel/locking/lockdep.c
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@ -1838,10 +1838,37 @@ static inline bool class_equal(struct lock_list *entry, void *data)
return entry->class == data; return entry->class == data;
} }
/*
* We are about to add B -> A into the dependency graph, and in __bfs() a
* strong dependency path A -> .. -> B is found: hlock_class equals
* entry->class.
*
* We will have a deadlock case (conflict) if A -> .. -> B -> A is a strong
* dependency cycle, that means:
*
* Either
*
* a) B -> A is -(E*)->
*
* or
*
* b) A -> .. -> B is -(*N)-> (i.e. A -> .. -(*N)-> B)
*
* as then we don't have -(*R)-> -(S*)-> in the cycle.
*/
static inline bool hlock_conflict(struct lock_list *entry, void *data)
{
struct held_lock *hlock = (struct held_lock *)data;
return hlock_class(hlock) == entry->class && /* Found A -> .. -> B */
(hlock->read == 0 || /* B -> A is -(E*)-> */
!entry->only_xr); /* A -> .. -> B is -(*N)-> */
}
static noinline void print_circular_bug(struct lock_list *this, static noinline void print_circular_bug(struct lock_list *this,
struct lock_list *target, struct lock_list *target,
struct held_lock *check_src, struct held_lock *check_src,
struct held_lock *check_tgt) struct held_lock *check_tgt)
{ {
struct task_struct *curr = current; struct task_struct *curr = current;
struct lock_list *parent; struct lock_list *parent;
@ -1950,13 +1977,13 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
* <target> or not. * <target> or not.
*/ */
static noinline enum bfs_result static noinline enum bfs_result
check_path(struct lock_class *target, struct lock_list *src_entry, check_path(struct held_lock *target, struct lock_list *src_entry,
bool (*match)(struct lock_list *entry, void *data),
struct lock_list **target_entry) struct lock_list **target_entry)
{ {
enum bfs_result ret; enum bfs_result ret;
ret = __bfs_forwards(src_entry, (void *)target, class_equal, ret = __bfs_forwards(src_entry, target, match, target_entry);
target_entry);
if (unlikely(bfs_error(ret))) if (unlikely(bfs_error(ret)))
print_bfs_bug(ret); print_bfs_bug(ret);
@ -1983,7 +2010,7 @@ check_noncircular(struct held_lock *src, struct held_lock *target,
debug_atomic_inc(nr_cyclic_checks); debug_atomic_inc(nr_cyclic_checks);
ret = check_path(hlock_class(target), &src_entry, &target_entry); ret = check_path(target, &src_entry, hlock_conflict, &target_entry);
if (unlikely(ret == BFS_RMATCH)) { if (unlikely(ret == BFS_RMATCH)) {
if (!*trace) { if (!*trace) {
@ -2021,7 +2048,7 @@ check_redundant(struct held_lock *src, struct held_lock *target)
debug_atomic_inc(nr_redundant_checks); debug_atomic_inc(nr_redundant_checks);
ret = check_path(hlock_class(target), &src_entry, &target_entry); ret = check_path(target, &src_entry, class_equal, &target_entry);
if (ret == BFS_RMATCH) if (ret == BFS_RMATCH)
debug_atomic_inc(nr_redundant); debug_atomic_inc(nr_redundant);