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Date: Fri, 28 Feb 2020 14:15:42 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
oleksandr@...hat.com, Tim Murray <timmurray@...gle.com>,
Daniel Colascione <dancol@...gle.com>,
Sandeep Patil <sspatil@...gle.com>,
Sonny Rao <sonnyrao@...gle.com>,
Brian Geffon <bgeffon@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Johannes Weiner <hannes@...xchg.org>,
Shakeel Butt <shakeelb@...gle.com>,
John Dias <joaodias@...gle.com>,
Joel Fernandes <joel@...lfernandes.org>, sj38.park@...il.com,
alexander.h.duyck@...ux.intel.com, Jann Horn <jannh@...gle.com>,
Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v6 1/7] mm: pass task and mm to do_madvise
On Tue, Feb 18, 2020 at 5:44 PM Minchan Kim <minchan@...nel.org> wrote:
>
> In upcoming patches, do_madvise will be called from external process
> context so we shouldn't asssume "current" is always hinted process's
> task_struct. Furthermore, we couldn't access mm_struct via task->mm
> once it's verified by access_mm which will be introduced in next
> patch[1]. And let's pass *current* and current->mm as arguments of
> do_madvise so it shouldn't change existing behavior but prepare
> next patch to make review easy.
>
> Note: io_madvise pass NULL as target_task argument of do_madvise
> because it couldn't know who is target.
>
> [1] http://lore.kernel.org/r/CAG48ez27=pwm5m_N_988xT1huO7g7h6arTQL44zev6TD-h-7Tg@mail.gmail.com
>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Jann Horn <jannh@...gle.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> fs/io_uring.c | 2 +-
> include/linux/mm.h | 3 ++-
> mm/madvise.c | 34 +++++++++++++++++++---------------
> 3 files changed, 22 insertions(+), 17 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 63beda9bafc5..a858da2ae2f4 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2736,7 +2736,7 @@ static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt,
> if (force_nonblock)
> return -EAGAIN;
>
> - ret = do_madvise(ma->addr, ma->len, ma->advice);
> + ret = do_madvise(NULL, req->work.mm, ma->addr, ma->len, ma->advice);
> if (ret < 0)
> req_set_fail_links(req);
> io_cqring_add_event(req, ret);
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 52269e56c514..bc16c8774328 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2323,7 +2323,8 @@ extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
> struct list_head *uf, bool downgrade);
> extern int do_munmap(struct mm_struct *, unsigned long, size_t,
> struct list_head *uf);
> -extern int do_madvise(unsigned long start, size_t len_in, int behavior);
> +extern int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
> + unsigned long start, size_t len_in, int behavior);
>
> static inline unsigned long
> do_mmap_pgoff(struct file *file, unsigned long addr,
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 43b47d3fae02..f75c86b6c463 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -254,6 +254,7 @@ static long madvise_willneed(struct vm_area_struct *vma,
> struct vm_area_struct **prev,
> unsigned long start, unsigned long end)
> {
> + struct mm_struct *mm = vma->vm_mm;
> struct file *file = vma->vm_file;
> loff_t offset;
>
> @@ -288,12 +289,12 @@ static long madvise_willneed(struct vm_area_struct *vma,
> */
> *prev = NULL; /* tell sys_madvise we drop mmap_sem */
> get_file(file);
> - up_read(¤t->mm->mmap_sem);
> + up_read(&mm->mmap_sem);
> offset = (loff_t)(start - vma->vm_start)
> + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
> vfs_fadvise(file, offset, end - start, POSIX_FADV_WILLNEED);
> fput(file);
> - down_read(¤t->mm->mmap_sem);
> + down_read(&mm->mmap_sem);
> return 0;
> }
>
> @@ -676,7 +677,6 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> if (nr_swap) {
> if (current->mm == mm)
> sync_mm_rss(mm);
> -
> add_mm_counter(mm, MM_SWAPENTS, nr_swap);
> }
> arch_leave_lazy_mmu_mode();
> @@ -756,6 +756,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
> unsigned long start, unsigned long end,
> int behavior)
> {
> + struct mm_struct *mm = vma->vm_mm;
> +
> *prev = vma;
> if (!can_madv_lru_vma(vma))
> return -EINVAL;
> @@ -763,8 +765,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
> if (!userfaultfd_remove(vma, start, end)) {
> *prev = NULL; /* mmap_sem has been dropped, prev is stale */
>
> - down_read(¤t->mm->mmap_sem);
> - vma = find_vma(current->mm, start);
> + down_read(&mm->mmap_sem);
> + vma = find_vma(mm, start);
> if (!vma)
> return -ENOMEM;
> if (start < vma->vm_start) {
> @@ -818,6 +820,7 @@ static long madvise_remove(struct vm_area_struct *vma,
> loff_t offset;
> int error;
> struct file *f;
> + struct mm_struct *mm = vma->vm_mm;
>
> *prev = NULL; /* tell sys_madvise we drop mmap_sem */
>
> @@ -845,13 +848,13 @@ static long madvise_remove(struct vm_area_struct *vma,
> get_file(f);
> if (userfaultfd_remove(vma, start, end)) {
> /* mmap_sem was not released by userfaultfd_remove() */
> - up_read(¤t->mm->mmap_sem);
> + up_read(&mm->mmap_sem);
> }
> error = vfs_fallocate(f,
> FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> offset, end - start);
> fput(f);
> - down_read(¤t->mm->mmap_sem);
> + down_read(&mm->mmap_sem);
> return error;
> }
>
> @@ -1044,7 +1047,8 @@ madvise_behavior_valid(int behavior)
> * -EBADF - map exists, but area maps something that isn't a file.
> * -EAGAIN - a kernel resource was temporarily unavailable.
> */
> -int do_madvise(unsigned long start, size_t len_in, int behavior)
> +int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
> + unsigned long start, size_t len_in, int behavior)
> {
> unsigned long end, tmp;
> struct vm_area_struct *vma, *prev;
> @@ -1082,10 +1086,10 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
>
> write = madvise_need_mmap_write(behavior);
> if (write) {
> - if (down_write_killable(¤t->mm->mmap_sem))
> + if (down_write_killable(&mm->mmap_sem))
> return -EINTR;
> } else {
> - down_read(¤t->mm->mmap_sem);
> + down_read(&mm->mmap_sem);
> }
>
> /*
> @@ -1093,7 +1097,7 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
> * ranges, just ignore them, but return -ENOMEM at the end.
> * - different from the way of handling in mlock etc.
> */
> - vma = find_vma_prev(current->mm, start, &prev);
> + vma = find_vma_prev(mm, start, &prev);
> if (vma && start > vma->vm_start)
> prev = vma;
>
> @@ -1130,19 +1134,19 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
> if (prev)
> vma = prev->vm_next;
> else /* madvise_remove dropped mmap_sem */
> - vma = find_vma(current->mm, start);
> + vma = find_vma(mm, start);
> }
> out:
> blk_finish_plug(&plug);
> if (write)
> - up_write(¤t->mm->mmap_sem);
> + up_write(&mm->mmap_sem);
> else
> - up_read(¤t->mm->mmap_sem);
> + up_read(&mm->mmap_sem);
>
> return error;
> }
>
> SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> {
> - return do_madvise(start, len_in, behavior);
> + return do_madvise(current, current->mm, start, len_in, behavior);
> }
> --
> 2.25.0.265.gbab2e86ba0-goog
>
Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
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