> On Sep 12, 2023, at 9:15 AM, Matthieu Baerts <[email protected]>
> wrote:
> Hi Catalin,
>
> On 06/09/2023 19:15, Catalin Marinas wrote:
>
> (...)
>
>> I had a patch already but got distracted by a few (real) leaks reported
>> while testing it. Feel free to pick it up and change _ignore to
>> _not_leak if you find that more suitable. Well, it would be good for
>> Christoph to test it as I haven't managed to reproduce the false
>> positive.
>
> Thank you for the patch!
>
>> ----------------------8<--------------------------
>> From b25350cb6f8a906a6164b625bfd57021190cb105 Mon Sep 17 00:00:00 2001
>> From: Catalin Marinas <[email protected]>
>> Date: Wed, 6 Sep 2023 17:52:45 +0100
>> Subject: [PATCH] rcu: kmemleak: Ignore kmemleak false positives when
>> RCU-freeing objects
>>
>> Since the actual slab freeing is deferred when calling kvfree_rcu(), so
>> is the kmemleak_free() callback informing kmemleak of the object
>> deletion. From the perspective of the kvfree_rcu() caller, the object is
>> freed and it may remove any references to it. Since kmemleak does not
>> scan the tree RCU internal data storing the pointer, it will report such
>> objects as leaks during the grace period.
>>
>> Tell kmemleak to ignore such objects on the kvfree_call_rcu() path. Note
>> that the tiny RCU implementation does not have such issue since the
>> objects can be tracked from the rcu_ctrlblk structure.
>>
>> Signed-off-by: Catalin Marinas <[email protected]>
>> Reported-by: Christoph Paasch <[email protected]>
>> ---
>> kernel/rcu/tree.c | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>>
>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>> index cb1caefa8bd0..2ac39b5705df 100644
>> --- a/kernel/rcu/tree.c
>> +++ b/kernel/rcu/tree.c
>> @@ -31,6 +31,7 @@
>> #include <linux/bitops.h>
>> #include <linux/export.h>
>> #include <linux/completion.h>
>> +#include <linux/kmemleak.h>
>> #include <linux/moduleparam.h>
>> #include <linux/panic.h>
>> #include <linux/panic_notifier.h>
>> @@ -3388,6 +3389,14 @@ void kvfree_call_rcu(struct rcu_head *head, void *ptr)
>> success = true;
>> }
>>
>> + /*
>> + * The kvfree_rcu() caller considers the pointer freed at this point
>> + * and likely removes any references to it. Since the the actual slab
>
> Just in case you didn't send this patch, checkpatch.pl noticed that the
> word "the" was repeated in the comment here above ("Since the the actual").
Sounds like you detected a leak in the word the. :-)
(Sorry could not resist).
- Joel
>
> Cheers,
> Matt
>
>> + * freeing (and kmemleak_free()) is deferred, tell kmemleak to ignore
>> + * this object (no scanning or false positives reporting).
>> + */
>> + kmemleak_ignore(ptr);
>> +
>> // Set timer to drain after KFREE_DRAIN_JIFFIES.
>> if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING)
>> schedule_delayed_monitor_work(krcp);
>
> --
> Tessares | Belgium | Hybrid Access Solutions
> www.tessares.net
