linux-kernel - Re: [PATCH 13/13] rcu/kvfree: Eliminate k[v]free

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Message-Id: <A3933CE1-1C8A-4E9B-9E10-828CB2CE34AA@joelfernandes.org>
Date:   Sun, 5 Mar 2023 05:49:35 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>,
        Jens Axboe <axboe@...nel.dk>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        Bryan Tan <bryantan@...are.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Bob Pearson <rpearsonhpe@...il.com>,
        Ariel Levkovich <lariel@...dia.com>,
        Theodore Ts'o <tytso@....edu>, Julian Anastasov <ja@....bg>
Subject: Re: [PATCH 13/13] rcu/kvfree: Eliminate k[v]free_rcu() single argument macro



> On Mar 5, 2023, at 5:29 AM, Joel Fernandes <joel@...lfernandes.org> wrote:
> 
> Hi, All,
> 
>> On Wed, Feb 1, 2023 at 10:11 AM Uladzislau Rezki (Sony)
>> <urezki@...il.com> wrote:
>> 
>> For a single argument invocations a new kfree_rcu_mightsleep()
>> and kvfree_rcu_mightsleep() macroses are used. This is done in
>> order to prevent users from calling a single argument from
>> atomic contexts as "_mightsleep" prefix signals that it can
>> schedule().
>> 
> 
> Since this commit in -dev branch [1] suggests more users still need
> conversion, let us drop this single patch for 6.4 and move the rest of
> the series forward? Let me know if you disagree.
> https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=dev&id=9bf5e3a2626ed474d080f695007541b6ecd6e60b
> 
> All -- please supply Ack/Review tags for patches 1-12.

Or put another way, what is the transition plan for these remaining users?

I am getting on a plane right now but I can research which users are remaining later.

 - Joel


> 
> thanks,
> 
> - Joel
> 
> 
>> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
>> ---
>> include/linux/rcupdate.h | 29 ++++++++---------------------
>> 1 file changed, 8 insertions(+), 21 deletions(-)
>> 
>> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
>> index 094321c17e48..7571dbfecb18 100644
>> --- a/include/linux/rcupdate.h
>> +++ b/include/linux/rcupdate.h
>> @@ -957,9 +957,8 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
>> 
>> /**
>>  * kfree_rcu() - kfree an object after a grace period.
>> - * @ptr: pointer to kfree for both single- and double-argument invocations.
>> - * @rhf: the name of the struct rcu_head within the type of @ptr,
>> - *       but only for double-argument invocations.
>> + * @ptr: pointer to kfree for double-argument invocations.
>> + * @rhf: the name of the struct rcu_head within the type of @ptr.
>>  *
>>  * Many rcu callbacks functions just call kfree() on the base structure.
>>  * These functions are trivial, but their size adds up, and furthermore
>> @@ -982,26 +981,18 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
>>  * The BUILD_BUG_ON check must not involve any function calls, hence the
>>  * checks are done in macros here.
>>  */
>> -#define kfree_rcu(ptr, rhf...) kvfree_rcu(ptr, ## rhf)
>> +#define kfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
>> +#define kvfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf)
>> 
>> /**
>> - * kvfree_rcu() - kvfree an object after a grace period.
>> - *
>> - * This macro consists of one or two arguments and it is
>> - * based on whether an object is head-less or not. If it
>> - * has a head then a semantic stays the same as it used
>> - * to be before:
>> - *
>> - *     kvfree_rcu(ptr, rhf);
>> - *
>> - * where @ptr is a pointer to kvfree(), @rhf is the name
>> - * of the rcu_head structure within the type of @ptr.
>> + * kfree_rcu_mightsleep() - kfree an object after a grace period.
>> + * @ptr: pointer to kfree for single-argument invocations.
>>  *
>>  * When it comes to head-less variant, only one argument
>>  * is passed and that is just a pointer which has to be
>>  * freed after a grace period. Therefore the semantic is
>>  *
>> - *     kvfree_rcu(ptr);
>> + *     kfree_rcu_mightsleep(ptr);
>>  *
>>  * where @ptr is the pointer to be freed by kvfree().
>>  *
>> @@ -1010,13 +1001,9 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
>>  * annotation. Otherwise, please switch and embed the
>>  * rcu_head structure within the type of @ptr.
>>  */
>> -#define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__,          \
>> -       kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
>> -
>> +#define kfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
>> #define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr)
>> -#define kfree_rcu_mightsleep(ptr) kvfree_rcu_mightsleep(ptr)
>> 
>> -#define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
>> #define kvfree_rcu_arg_2(ptr, rhf)                                     \
>> do {                                                                   \
>>        typeof (ptr) ___p = (ptr);                                      \
>> --
>> 2.30.2
>>