2021-02-12 23:32:22

by Shuah Khan

Subject: [PATCH 1/2] lockdep: add lockdep_assert_not_held()

Some kernel functions must not be called holding a specific lock. Doing
so could lead to locking problems. Currently these routines call
lock_is_held() to check for lock hold followed by WARN_ON.

Adding a common lockdep interface will help reduce the duplication of this
logic in the rest of the kernel.

Add lockdep_assert_not_held() to be used in these functions to detect
incorrect calls while holding a lock.

lockdep_assert_not_held() provides the opposite functionality of
lockdep_assert_held() which is used to assert calls that require
holding a specific lock.

The need for lockdep_assert_not_held() came up in a discussion on
ath10k patch. ath10k_drain_tx() and i915_vma_pin_ww() are examples
of functions that can use lockdep_assert_not_held().

Link: https://lore.kernel.org/linux-wireless/[email protected]/
Signed-off-by: Shuah Khan <[email protected]>
---
include/linux/lockdep.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b9e9adec73e8..567e3a1a27ce 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -294,6 +294,10 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);

#define lockdep_depth(tsk) (debug_locks ? (tsk)->lockdep_depth : 0)

+#define lockdep_assert_not_held(l) do { \
+ WARN_ON(debug_locks && lockdep_is_held(l)); \
+ } while (0)
+
#define lockdep_assert_held(l) do { \
WARN_ON(debug_locks && !lockdep_is_held(l)); \
} while (0)
@@ -383,8 +387,9 @@ extern int lock_is_held(const void *);
extern int lockdep_is_held(const void *);
#define lockdep_is_held_type(l, r) (1)

+#define lockdep_assert_not_held(l) do { (void)(l); } while (0)
#define lockdep_assert_held(l) do { (void)(l); } while (0)
-#define lockdep_assert_held_write(l) do { (void)(l); } while (0)
+#define lockdep_assert_held_write(l) do { (void)(l); } while (0)
#define lockdep_assert_held_read(l) do { (void)(l); } while (0)
#define lockdep_assert_held_once(l) do { (void)(l); } while (0)

--
2.27.0

2021-02-15 13:16:05

by Johannes Berg

Subject: Re: [PATCH 1/2] lockdep: add lockdep_assert_not_held()

On Mon, 2021-02-15 at 11:44 +0100, Peter Zijlstra wrote:
>
> I think something like so will work, but please double check.

Yeah, that looks better.

> +++ b/include/linux/lockdep.h
> @@ -294,11 +294,15 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
>
> #define lockdep_depth(tsk) (debug_locks ? (tsk)->lockdep_depth : 0)
>
> -#define lockdep_assert_held(l) do { \
> - WARN_ON(debug_locks && !lockdep_is_held(l)); \
> +#define lockdep_assert_held(l) do { \
> + WARN_ON(debug_locks && lockdep_is_held(l) == 0)); \
> } while (0)

That doesn't really need to change? It's the same.

> -#define lockdep_assert_held_write(l) do { \
> +#define lockdep_assert_not_held(l) do { \
> + WARN_ON(debug_locks && lockdep_is_held(l) == 1)); \
> + } while (0)
> +
> +#define lockdep_assert_held_write(l) do { \
> WARN_ON(debug_locks && !lockdep_is_held_type(l, 0)); \
> } while (0)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index c1418b47f625..983ba206f7b2 100644
> --- a/kernel/locking/lockdep.
> +++ b/kernel/locking/lockdep.c
> @@ -5467,7 +5467,7 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
> int ret = 0;
>
> if (unlikely(!lockdep_enabled()))
> - return 1; /* avoid false negative lockdep_assert_held() */
> + return -1; /* avoid false negative lockdep_assert_held() */

Maybe add lockdep_assert_not_held() to the comment, to explain the -1
(vs non-zero)?

johannes