2021-02-12 23:30:07

by Shuah Khan

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Subject: [PATCH 0/2] 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]/

This patch series adds lockdep_assert_not_held() and uses it in the
second patch in ath10k_drain_tx() function.

Shuah Khan (2):
lockdep: add lockdep_assert_not_held()
ath10k: detect conf_mutex held ath10k_drain_tx() calls

drivers/net/wireless/ath/ath10k/mac.c | 2 ++
include/linux/lockdep.h | 7 ++++++-
2 files changed, 8 insertions(+), 1 deletion(-)


2021-02-12 23:31:24

by Shuah Khan

[permalink] [raw]
Subject: [PATCH 2/2] ath10k: detect conf_mutex held ath10k_drain_tx() calls

ath10k_drain_tx() must not be called with conf_mutex held as workers can
use that also. Add call to lockdep_assert_not_held() on conf_mutex to
detect if conf_mutex is held by the caller.

The idea for this patch stemmed from coming across the comment block
above the ath10k_drain_tx() while reviewing the conf_mutex holds during
to debug the conf_mutex lock assert in ath10k_debug_fw_stats_request().

Adding detection to assert on conf_mutex hold will help detect incorrect
usages that could lead to locking problems when async worker routines try
to call this routine.

Link: https://lore.kernel.org/linux-wireless/[email protected]/
Signed-off-by: Shuah Khan <[email protected]>
drivers/net/wireless/ath/ath10k/mac.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/ath/ath10k/mac.c
index c202b167d8c6..7de05b679ad2 100644
--- a/drivers/net/wireless/ath/ath10k/mac.c
+++ b/drivers/net/wireless/ath/ath10k/mac.c
@@ -4728,6 +4728,8 @@ static void ath10k_mac_op_wake_tx_queue(struct ieee80211_hw *hw,
/* Must not be called with conf_mutex held as workers can use that also. */
void ath10k_drain_tx(struct ath10k *ar)
+ lockdep_assert_not_held(&ar->conf_mutex);
/* make sure rcu-protected mac80211 tx path itself is drained */