lkml.org 
[lkml]   [2021]   [Feb]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 4/5] ath10k: detect conf_mutex held ath10k_drain_tx() calls
From
Date
On 2/10/21 1:25 AM, Kalle Valo wrote:
> Shuah Khan <skhan@linuxfoundation.org> writes:
>
>> ath10k_drain_tx() must not be called with conf_mutex held as workers can
>> use that also. Add check to detect conf_mutex held calls.
>>
>> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
>
> The commit log does not answer to "Why?". How did you find this? What
> actual problem are you trying to solve?
>

I came across the comment block above the ath10k_drain_tx() as I was
reviewing at conf_mutex holds while I was debugging the conf_mutex
lock assert in ath10k_debug_fw_stats_request().

My reasoning is that having this will help detect incorrect usages
of ath10k_drain_tx() while holding conf_mutex which could lead to
locking problems when async worker routines try to call this routine.

>> ---
>> drivers/net/wireless/ath/ath10k/mac.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/ath/ath10k/mac.c
>> index 53f92945006f..3545ce7dce0a 100644
>> --- a/drivers/net/wireless/ath/ath10k/mac.c
>> +++ b/drivers/net/wireless/ath/ath10k/mac.c
>> @@ -4566,6 +4566,7 @@ 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)
>> {
>> + WARN_ON(lockdep_is_held(&ar->conf_mutex));
>
> Empty line after WARN_ON().
>

Will do.

> Shouldn't this check debug_locks similarly lockdep_assert_held() does?
>
> #define lockdep_assert_held(l) do { \
> WARN_ON(debug_locks && !lockdep_is_held(l)); \
> } while (0)
>
> And I suspect you need #ifdef CONFIG_LOCKDEP which should fix the kbuild
> bot error.
>

Yes.

> But honestly I would prefer to have lockdep_assert_not_held() in
> include/linux/lockdep.h, much cleaner that way. Also
> i915_gem_object_lookup_rcu() could then use the same macro.
>

Right. This is the right way to go. That was first instinct and
decided to have the discussion evolve in that direction. Now that
it has, I will combine this change with
include/linux/lockdep.h and add lockdep_assert_not_held()

I think we might have other places in the kernel that could use
lockdep_assert_not_held() in addition to i915_gem_object_lookup_rcu()

thanks,
-- Shuah

\
 
 \ /
  Last update: 2021-02-10 16:59    [W:0.176 / U:0.188 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site