Re: [PATCH RFC V2] mm: convert rcu_read_lock() to srcu_read_lock(), thus allowing to sleep in callbacks

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

sagig wrote:
> Hey Konstantin,
> Do you have any comments on V2?

only one, below.

>
> On 2/6/2012 4:40 PM, sagig@mellanox.com wrote:
>> From: Sagi Grimberg<sagig@mellanox.co.il>
>>
>> Now that anon_vma lock and i_mmap_mutex are both sleepable mutex, it is possible to schedule inside invalidation callbacks
>> (such as invalidate_page, invalidate_range_start/end and change_pte) .
>> This is essential for a scheduling HW sync in RDMA drivers which apply on demand paging methods.
>>
>> Signed-off-by: Sagi Grimberg<sagig@mellanox.co.il>
>> ---
>>    changes from V1:
>>    1. converted synchronize_rcu() to synchronize_srcu() to racing candidates (unregister, release)
>>    2. do_mmu_notifier_register: moved init_srcu_struct out of mmap_sem locking.
>>    3. do_mmu_notifier_register: fixed error path.
>>
>>    include/linux/mmu_notifier.h |    3 +++
>>    mm/mmu_notifier.c            |   38 +++++++++++++++++++++++++-------------
>>    2 files changed, 28 insertions(+), 13 deletions(-)
>>
>> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
>> index 1d1b1e1..f3d6f30 100644
>> --- a/include/linux/mmu_notifier.h
>> +++ b/include/linux/mmu_notifier.h

>> @@ -226,8 +233,12 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
>>    out_cleanup:
>>    	if (take_mmap_sem)
>>    		up_write(&mm->mmap_sem);
>> -	/* kfree() does nothing if mmu_notifier_mm is NULL */
>> -	kfree(mmu_notifier_mm);
>> +
>> +	if (mm->mmu_notifier_mm) {
>> +		/* in the case srcu_init failed srcu_cleanup is safe */
>> +		cleanup_srcu_struct(&mm->mmu_notifier_mm->srcu);
>> +		kfree(mmu_notifier_mm);
>> +	}

this seems incorrect. there must be:

if (mmu_notifier_mm) {
	cleanup_srcu_struct(&mmu_notifier_mm->srcu);
	kfree(mmu_notifier_mm);
}

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