[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <61c05197-0baa-4680-ad24-5965ba37dc35@redhat.com>
Date: Wed, 21 Aug 2024 11:53:14 +0200
From: David Hildenbrand <david@...hat.com>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: LEROY Christophe <christophe.leroy2@...soprasteria.com>,
"hughd@...gle.com" <hughd@...gle.com>,
"willy@...radead.org" <willy@...radead.org>,
"muchun.song@...ux.dev" <muchun.song@...ux.dev>,
"vbabka@...nel.org" <vbabka@...nel.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"rppt@...nel.org" <rppt@...nel.org>,
"vishal.moola@...il.com" <vishal.moola@...il.com>,
"peterx@...hat.com" <peterx@...hat.com>,
"ryan.roberts@....com" <ryan.roberts@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 06/14] mm: handle_pte_fault() use
pte_offset_map_maywrite_nolock()
On 21.08.24 11:51, Qi Zheng wrote:
>
>
> On 2024/8/21 17:41, David Hildenbrand wrote:
>> On 21.08.24 11:24, Qi Zheng wrote:
>>>
>>>
>>> On 2024/8/21 17:17, LEROY Christophe wrote:
>>>>
>>>>
>>>> Le 21/08/2024 à 10:18, Qi Zheng a écrit :
>>>>> In handle_pte_fault(), we may modify the vmf->pte after acquiring the
>>>>> vmf->ptl, so convert it to using pte_offset_map_maywrite_nolock(). But
>>>>> since we already do the pte_same() check, so there is no need to get
>>>>> pmdval to do pmd_same() check, just pass NULL to pmdvalp parameter.
>>>>>
>>>>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
>>>>> ---
>>>>> mm/memory.c | 9 +++++++--
>>>>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/mm/memory.c b/mm/memory.c
>>>>> index 93c0c25433d02..d3378e98faf13 100644
>>>>> --- a/mm/memory.c
>>>>> +++ b/mm/memory.c
>>>>> @@ -5504,9 +5504,14 @@ static vm_fault_t handle_pte_fault(struct
>>>>> vm_fault *vmf)
>>>>> * pmd by anon khugepaged, since that takes mmap_lock in
>>>>> write
>>>>> * mode; but shmem or file collapse to THP could still
>>>>> morph
>>>>> * it into a huge pmd: just retry later if so.
>>>>> + *
>>>>> + * Use the maywrite version to indicate that vmf->pte will be
>>>>> + * modified, but since we will use pte_same() to detect the
>>>>> + * change of the pte entry, there is no need to get pmdval.
>>>>> */
>>>>> - vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm, vmf->pmd,
>>>>> - vmf->address, &vmf->ptl);
>>>>> + vmf->pte = pte_offset_map_maywrite_nolock(vmf->vma->vm_mm,
>>>>> + vmf->pmd, vmf->address,
>>>>> + NULL, &vmf->ptl);
>>
>> I think we discussed that passing NULL should be forbidden for that
>> function.
>
> Yes, but for some maywrite case, there is no need to get pmdval to
> do pmd_same() check. So I passed NULL and added a comment to
> explain this.
I wonder if it's better to pass a dummy variable instead. One has to
think harder why that is required compared to blindly passing "NULL" :)
--
Cheers,
David / dhildenb
Powered by blists - more mailing lists