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SubjectRe: [PATCH 4/5] mm/hmm: hmm_vma_fault() doesn't always call hmm_range_unregister()
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On 5/7/19 6:15 AM, Souptick Joarder wrote:
> On Tue, May 7, 2019 at 5:00 AM <rcampbell@nvidia.com> wrote:
>>
>> From: Ralph Campbell <rcampbell@nvidia.com>
>>
>> The helper function hmm_vma_fault() calls hmm_range_register() but is
>> missing a call to hmm_range_unregister() in one of the error paths.
>> This leads to a reference count leak and ultimately a memory leak on
>> struct hmm.
>>
>> Always call hmm_range_unregister() if hmm_range_register() succeeded.
>
> How about * Call hmm_range_unregister() in error path if
> hmm_range_register() succeeded* ?

Sure, sounds good.
I'll include that in v2.

>>
>> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
>> Cc: John Hubbard <jhubbard@nvidia.com>
>> Cc: Ira Weiny <ira.weiny@intel.com>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Cc: Arnd Bergmann <arnd@arndb.de>
>> Cc: Balbir Singh <bsingharora@gmail.com>
>> Cc: Dan Carpenter <dan.carpenter@oracle.com>
>> Cc: Matthew Wilcox <willy@infradead.org>
>> Cc: Souptick Joarder <jrdr.linux@gmail.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> ---
>> include/linux/hmm.h | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
>> index 35a429621e1e..fa0671d67269 100644
>> --- a/include/linux/hmm.h
>> +++ b/include/linux/hmm.h
>> @@ -559,6 +559,7 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block)
>> return (int)ret;
>>
>> if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
>> + hmm_range_unregister(range);
>> /*
>> * The mmap_sem was taken by driver we release it here and
>> * returns -EAGAIN which correspond to mmap_sem have been
>> @@ -570,13 +571,13 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block)
>>
>> ret = hmm_range_fault(range, block);
>> if (ret <= 0) {
>> + hmm_range_unregister(range);
>
> what is the reason to moved it up ?

I moved it up because the normal calling pattern is:
down_read(&mm->mmap_sem)
hmm_vma_fault()
hmm_range_register()
hmm_range_fault()
hmm_range_unregister()
up_read(&mm->mmap_sem)

I don't think it is a bug to unlock mmap_sem and then unregister,
it is just more consistent nesting.

>> if (ret == -EBUSY || !ret) {
>> /* Same as above, drop mmap_sem to match old API. */
>> up_read(&range->vma->vm_mm->mmap_sem);
>> ret = -EBUSY;
>> } else if (ret == -EAGAIN)
>> ret = -EBUSY;
>> - hmm_range_unregister(range);
>> return ret;
>> }
>> return 0;
>> --
>> 2.20.1
>>

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