* [PATCH v4] workqueue: Remove unnecessary kfree(NULL)
@ 2020-05-27 1:50 qiang.zhang
2020-05-27 6:40 ` Markus Elfring
0 siblings, 1 reply; 3+ messages in thread
From: qiang.zhang @ 2020-05-27 1:50 UTC (permalink / raw)
To: tj; +Cc: jiangshanlai, markus.elfring, linux-kernel
From: Zhang Qiang <qiang.zhang@windriver.com>
The callback function "rcu_free_wq" could be called after memory
was released for "wq->rescuer" already and assignment is empty. so
remove unnecessary kfree(NULL).
Fixes: def98c84b6cd ("workqueue: Fix spurious sanity check failures in destroy_workqueue()")
Fixes: 8efe1223d73c ("workqueue: Fix missing kfree(rescuer) in destroy_workqueue()")
Signed-off-by: Zhang Qiang <qiang.zhang@windriver.com>
---
v1->v2->v3->v4:
Modify wrong submission information.
kernel/workqueue.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 891ccad5f271..a2451cdcd503 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3491,7 +3491,6 @@ static void rcu_free_wq(struct rcu_head *rcu)
else
free_workqueue_attrs(wq->unbound_attrs);
- kfree(wq->rescuer);
kfree(wq);
}
--
2.24.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v4] workqueue: Remove unnecessary kfree() call in rcu_free_wq()
2020-05-27 1:50 [PATCH v4] workqueue: Remove unnecessary kfree(NULL) qiang.zhang
@ 2020-05-27 6:40 ` Markus Elfring
0 siblings, 0 replies; 3+ messages in thread
From: Markus Elfring @ 2020-05-27 6:40 UTC (permalink / raw)
To: Zhang Qiang, Tejun Heo, Lai Jiangshan; +Cc: linux-kernel, kernel-janitors
> The callback function "rcu_free_wq" could be called after memory
> was released for "wq->rescuer" already and assignment is empty. so
> remove unnecessary kfree(NULL).
I have got the impression that also this wording approach contains weaknesses.
How do you think about a wording variant like the following?
The data structure member “wq->rescuer” was reset to a null pointer
in one if branch. It was passed to a call of the function “kfree”
in the callback function “rcu_free_wq” (which was eventually executed).
The function “kfree” does not perform more meaningful data processing
for a passed null pointer (besides immediately returning from such a call).
Thus delete this function call which became unnecessary with the referenced
software update.
> Fixes: def98c84b6cd ("workqueue: Fix spurious sanity check failures in destroy_workqueue()")
This change triggered another collateral evolution finally.
Would you like to detect similarly questionable function calls
by advanced source code analysis?
> Fixes: 8efe1223d73c ("workqueue: Fix missing kfree(rescuer) in destroy_workqueue()")
Please delete this tag from the change description
(because I find that it is not so relevant here.)
> v1->v2->v3->v4:
> Modify wrong submission information.
Will it be nicer to mention the adjustment of the commit message?
Regards,
Markus
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v4] workqueue: Remove unnecessary kfree() call in rcu_free_wq()
@ 2020-05-27 6:40 ` Markus Elfring
0 siblings, 0 replies; 3+ messages in thread
From: Markus Elfring @ 2020-05-27 6:40 UTC (permalink / raw)
To: Zhang Qiang, Tejun Heo, Lai Jiangshan; +Cc: linux-kernel, kernel-janitors
> The callback function "rcu_free_wq" could be called after memory
> was released for "wq->rescuer" already and assignment is empty. so
> remove unnecessary kfree(NULL).
I have got the impression that also this wording approach contains weaknesses.
How do you think about a wording variant like the following?
The data structure member “wq->rescuer” was reset to a null pointer
in one if branch. It was passed to a call of the function “kfree”
in the callback function “rcu_free_wq” (which was eventually executed).
The function “kfree” does not perform more meaningful data processing
for a passed null pointer (besides immediately returning from such a call).
Thus delete this function call which became unnecessary with the referenced
software update.
> Fixes: def98c84b6cd ("workqueue: Fix spurious sanity check failures in destroy_workqueue()")
This change triggered another collateral evolution finally.
Would you like to detect similarly questionable function calls
by advanced source code analysis?
> Fixes: 8efe1223d73c ("workqueue: Fix missing kfree(rescuer) in destroy_workqueue()")
Please delete this tag from the change description
(because I find that it is not so relevant here.)
> v1->v2->v3->v4:
> Modify wrong submission information.
Will it be nicer to mention the adjustment of the commit message?
Regards,
Markus
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-05-27 6:40 UTC | newest]
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2020-05-27 1:50 [PATCH v4] workqueue: Remove unnecessary kfree(NULL) qiang.zhang
2020-05-27 6:40 ` [PATCH v4] workqueue: Remove unnecessary kfree() call in rcu_free_wq() Markus Elfring
2020-05-27 6:40 ` Markus Elfring
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