Re: [PATCH v2 1/7] mm/gup: Rename "nonblocking" to "locked" where proper

From: David Hildenbrand
Date: Fri Sep 06 2019 - 04:50:54 EST

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In reply to: Peter Xu: "[PATCH v2 1/7] mm/gup: Rename "nonblocking" to "locked" where proper"
Next in thread: Peter Xu: "[PATCH v2 2/7] mm: Introduce FAULT_FLAG_DEFAULT"
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On 05.09.19 12:15, Peter Xu wrote:
> There's plenty of places around __get_user_pages() that has a parameter
> "nonblocking" which does not really mean that "it won't block" (because
> it can really block) but instead it shows whether the mmap_sem is
> released by up_read() during the page fault handling mostly when
> VM_FAULT_RETRY is returned.
>
> We have the correct naming in e.g. get_user_pages_locked() or
> get_user_pages_remote() as "locked", however there're still many places
> that are using the "nonblocking" as name.
>
> Renaming the places to "locked" where proper to better suite the
> functionality of the variable. While at it, fixing up some of the
> comments accordingly.
>
> Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Jerome Glisse <jglisse@xxxxxxxxxx>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
> mm/gup.c | 44 +++++++++++++++++++++-----------------------
> mm/hugetlb.c | 8 ++++----
> 2 files changed, 25 insertions(+), 27 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 98f13ab37bac..eddbb95dcb8f 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -622,12 +622,12 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
> }
>
> /*
> - * mmap_sem must be held on entry. If @nonblocking != NULL and
> - * *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
> - * If it is, *@nonblocking will be set to 0 and -EBUSY returned.
> + * mmap_sem must be held on entry. If @locked != NULL and *@flags
> + * does not include FOLL_NOWAIT, the mmap_sem may be released. If it
> + * is, *@locked will be set to 0 and -EBUSY returned.
> */
> static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
> - unsigned long address, unsigned int *flags, int *nonblocking)
> + unsigned long address, unsigned int *flags, int *locked)
> {
> unsigned int fault_flags = 0;
> vm_fault_t ret;
> @@ -639,7 +639,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
> fault_flags |= FAULT_FLAG_WRITE;
> if (*flags & FOLL_REMOTE)
> fault_flags |= FAULT_FLAG_REMOTE;
> - if (nonblocking)
> + if (locked)
> fault_flags |= FAULT_FLAG_ALLOW_RETRY;
> if (*flags & FOLL_NOWAIT)
> fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
> @@ -665,8 +665,8 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
> }
>
> if (ret & VM_FAULT_RETRY) {
> - if (nonblocking && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
> - *nonblocking = 0;
> + if (locked && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
> + *locked = 0;
> return -EBUSY;
> }
>
> @@ -743,7 +743,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
> * only intends to ensure the pages are faulted in.
> * @vmas: array of pointers to vmas corresponding to each page.
> * Or NULL if the caller does not require them.
> - * @nonblocking: whether waiting for disk IO or mmap_sem contention
> + * @locked: whether we're still with the mmap_sem held
> *
> * Returns number of pages pinned. This may be fewer than the number
> * requested. If nr_pages is 0 or negative, returns 0. If no pages
> @@ -772,13 +772,11 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
> * appropriate) must be called after the page is finished with, and
> * before put_page is called.
> *
> - * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
> - * or mmap_sem contention, and if waiting is needed to pin all pages,
> - * *@nonblocking will be set to 0. Further, if @gup_flags does not
> - * include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
> - * this case.
> + * If @locked != NULL, *@locked will be set to 0 when mmap_sem is
> + * released by an up_read(). That can happen if @gup_flags does not
> + * have FOLL_NOWAIT.
> *
> - * A caller using such a combination of @nonblocking and @gup_flags
> + * A caller using such a combination of @locked and @gup_flags
> * must therefore hold the mmap_sem for reading only, and recognize
> * when it's been released. Otherwise, it must be held for either
> * reading or writing and will not be released.
> @@ -790,7 +788,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
> static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> unsigned long start, unsigned long nr_pages,
> unsigned int gup_flags, struct page **pages,
> - struct vm_area_struct **vmas, int *nonblocking)
> + struct vm_area_struct **vmas, int *locked)
> {
> long ret = 0, i = 0;
> struct vm_area_struct *vma = NULL;
> @@ -834,7 +832,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> if (is_vm_hugetlb_page(vma)) {
> i = follow_hugetlb_page(mm, vma, pages, vmas,
> &start, &nr_pages, i,
> - gup_flags, nonblocking);
> + gup_flags, locked);
> continue;
> }
> }
> @@ -852,7 +850,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> page = follow_page_mask(vma, start, foll_flags, &ctx);
> if (!page) {
> ret = faultin_page(tsk, vma, start, &foll_flags,
> - nonblocking);
> + locked);
> switch (ret) {
> case 0:
> goto retry;
> @@ -1178,7 +1176,7 @@ EXPORT_SYMBOL(get_user_pages_remote);
> * @vma: target vma
> * @start: start address
> * @end: end address
> - * @nonblocking:
> + * @locked: whether the mmap_sem is still held
> *
> * This takes care of mlocking the pages too if VM_LOCKED is set.
> *
> @@ -1186,14 +1184,14 @@ EXPORT_SYMBOL(get_user_pages_remote);
> *
> * vma->vm_mm->mmap_sem must be held.
> *
> - * If @nonblocking is NULL, it may be held for read or write and will
> + * If @locked is NULL, it may be held for read or write and will
> * be unperturbed.
> *
> - * If @nonblocking is non-NULL, it must held for read only and may be
> - * released. If it's released, *@nonblocking will be set to 0.
> + * If @locked is non-NULL, it must held for read only and may be
> + * released. If it's released, *@locked will be set to 0.
> */
> long populate_vma_page_range(struct vm_area_struct *vma,
> - unsigned long start, unsigned long end, int *nonblocking)
> + unsigned long start, unsigned long end, int *locked)
> {
> struct mm_struct *mm = vma->vm_mm;
> unsigned long nr_pages = (end - start) / PAGE_SIZE;
> @@ -1228,7 +1226,7 @@ long populate_vma_page_range(struct vm_area_struct *vma,
> * not result in a stack expansion that recurses back here.
> */
> return __get_user_pages(current, mm, start, nr_pages, gup_flags,
> - NULL, NULL, nonblocking);
> + NULL, NULL, locked);
> }
>
> /*
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index ede7e7f5d1ab..5f816ee42206 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4251,7 +4251,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
> long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> struct page **pages, struct vm_area_struct **vmas,
> unsigned long *position, unsigned long *nr_pages,
> - long i, unsigned int flags, int *nonblocking)
> + long i, unsigned int flags, int *locked)
> {
> unsigned long pfn_offset;
> unsigned long vaddr = *position;
> @@ -4322,7 +4322,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> spin_unlock(ptl);
> if (flags & FOLL_WRITE)
> fault_flags |= FAULT_FLAG_WRITE;
> - if (nonblocking)
> + if (locked)
> fault_flags |= FAULT_FLAG_ALLOW_RETRY;
> if (flags & FOLL_NOWAIT)
> fault_flags |= FAULT_FLAG_ALLOW_RETRY |
> @@ -4339,9 +4339,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> break;
> }
> if (ret & VM_FAULT_RETRY) {
> - if (nonblocking &&
> + if (locked &&
> !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
> - *nonblocking = 0;
> + *locked = 0;
> *nr_pages = 0;
> /*
> * VM_FAULT_RETRY must not return an
>

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

--

Thanks,

David / dhildenb

Next message: Masami Hiramatsu: "Re: [PATCH -tip v3 1/2] x86: xen: insn: Decode Xen and KVM emulate-prefix signature"
Previous message: John Garry: "Re: [PATCH 4/4] genirq: use irq's affinity for threaded irq with IRQF_RESCUE_THREAD"
In reply to: Peter Xu: "[PATCH v2 1/7] mm/gup: Rename "nonblocking" to "locked" where proper"
Next in thread: Peter Xu: "[PATCH v2 2/7] mm: Introduce FAULT_FLAG_DEFAULT"
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