Messages in this thread | | | Subject | Re: [PATCH v12 20/31] mm: introduce vma reference counter | From | Laurent Dufour <> | Date | Wed, 24 Apr 2019 16:26:06 +0200 |
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Le 22/04/2019 à 22:36, Jerome Glisse a écrit : > On Tue, Apr 16, 2019 at 03:45:11PM +0200, Laurent Dufour wrote: >> The final goal is to be able to use a VMA structure without holding the >> mmap_sem and to be sure that the structure will not be freed in our back. >> >> The lockless use of the VMA will be done through RCU protection and thus a >> dedicated freeing service is required to manage it asynchronously. >> >> As reported in a 2010's thread [1], this may impact file handling when a >> file is still referenced while the mapping is no more there. As the final >> goal is to handle anonymous VMA in a speculative way and not file backed >> mapping, we could close and free the file pointer in a synchronous way, as >> soon as we are guaranteed to not use it without holding the mmap_sem. For >> sanity reason, in a minimal effort, the vm_file file pointer is unset once >> the file pointer is put. >> >> [1] https://lore.kernel.org/linux-mm/20100104182429.833180340@chello.nl/ >> >> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com> > > Using kref would have been better from my POV even with RCU freeing > but anyway: > > Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Thanks Jérôme,
I think kref is a good option here, I'll give it a try.
>> --- >> include/linux/mm.h | 4 ++++ >> include/linux/mm_types.h | 3 +++ >> mm/internal.h | 27 +++++++++++++++++++++++++++ >> mm/mmap.c | 13 +++++++++---- >> 4 files changed, 43 insertions(+), 4 deletions(-) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index f14b2c9ddfd4..f761a9c65c74 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -529,6 +529,9 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm) >> vma->vm_mm = mm; >> vma->vm_ops = &dummy_vm_ops; >> INIT_LIST_HEAD(&vma->anon_vma_chain); >> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT >> + atomic_set(&vma->vm_ref_count, 1); >> +#endif >> } >> >> static inline void vma_set_anonymous(struct vm_area_struct *vma) >> @@ -1418,6 +1421,7 @@ static inline void INIT_VMA(struct vm_area_struct *vma) >> INIT_LIST_HEAD(&vma->anon_vma_chain); >> #ifdef CONFIG_SPECULATIVE_PAGE_FAULT >> seqcount_init(&vma->vm_sequence); >> + atomic_set(&vma->vm_ref_count, 1); >> #endif >> } >> >> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h >> index 24b3f8ce9e42..6a6159e11a3f 100644 >> --- a/include/linux/mm_types.h >> +++ b/include/linux/mm_types.h >> @@ -285,6 +285,9 @@ struct vm_area_struct { >> /* linked list of VM areas per task, sorted by address */ >> struct vm_area_struct *vm_next, *vm_prev; >> >> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT >> + atomic_t vm_ref_count; >> +#endif >> struct rb_node vm_rb; >> >> /* >> diff --git a/mm/internal.h b/mm/internal.h >> index 9eeaf2b95166..302382bed406 100644 >> --- a/mm/internal.h >> +++ b/mm/internal.h >> @@ -40,6 +40,33 @@ void page_writeback_init(void); >> >> vm_fault_t do_swap_page(struct vm_fault *vmf); >> >> + >> +extern void __free_vma(struct vm_area_struct *vma); >> + >> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT >> +static inline void get_vma(struct vm_area_struct *vma) >> +{ >> + atomic_inc(&vma->vm_ref_count); >> +} >> + >> +static inline void put_vma(struct vm_area_struct *vma) >> +{ >> + if (atomic_dec_and_test(&vma->vm_ref_count)) >> + __free_vma(vma); >> +} >> + >> +#else >> + >> +static inline void get_vma(struct vm_area_struct *vma) >> +{ >> +} >> + >> +static inline void put_vma(struct vm_area_struct *vma) >> +{ >> + __free_vma(vma); >> +} >> +#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */ >> + >> void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma, >> unsigned long floor, unsigned long ceiling); >> >> diff --git a/mm/mmap.c b/mm/mmap.c >> index f7f6027a7dff..c106440dcae7 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -188,6 +188,12 @@ static inline void mm_write_sequnlock(struct mm_struct *mm) >> } >> #endif /* CONFIG_SPECULATIVE_PAGE_FAULT */ >> >> +void __free_vma(struct vm_area_struct *vma) >> +{ >> + mpol_put(vma_policy(vma)); >> + vm_area_free(vma); >> +} >> + >> /* >> * Close a vm structure and free it, returning the next. >> */ >> @@ -200,8 +206,8 @@ static struct vm_area_struct *remove_vma(struct vm_area_struct *vma) >> vma->vm_ops->close(vma); >> if (vma->vm_file) >> fput(vma->vm_file); >> - mpol_put(vma_policy(vma)); >> - vm_area_free(vma); >> + vma->vm_file = NULL; >> + put_vma(vma); >> return next; >> } >> >> @@ -990,8 +996,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start, >> if (next->anon_vma) >> anon_vma_merge(vma, next); >> mm->map_count--; >> - mpol_put(vma_policy(next)); >> - vm_area_free(next); >> + put_vma(next); >> /* >> * In mprotect's case 6 (see comments on vma_merge), >> * we must remove another next too. It would clutter >> -- >> 2.21.0 >> >
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