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Date: Fri, 16 Dec 2016 10:26:40 +0100
From: Michal Hocko <mhocko@...nel.org>
To: Vegard Nossum <vegard.nossum@...cle.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Rik van Riel <riel@...hat.com>,
Matthew Wilcox <mawilcox@...rosoft.com>,
Peter Zijlstra <peterz@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Al Viro <viro@...iv.linux.org.uk>,
Ingo Molnar <mingo@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 2/4] mm: add new mmget() helper
On Fri 16-12-16 09:22:00, Vegard Nossum wrote:
> Apart from adding the helper function itself, the rest of the kernel is
> converted mechanically using:
>
> git grep -l 'atomic_inc.*mm_users' | xargs sed -i 's/atomic_inc(&\(.*\)->mm_users);/mmget\(\1\);/'
> git grep -l 'atomic_inc.*mm_users' | xargs sed -i 's/atomic_inc(&\(.*\)\.mm_users);/mmget\(\&\1\);/'
>
> This is needed for a later patch that hooks into the helper, but might be
> a worthwhile cleanup on its own.
Same here a clarification comment would be really nice
/**
* mmget: pins the address space
*
* Makes sure that the address space of the given mm struct doesn't go
* away. This doesn't protect from freeing parts of the address space
* though.
*
* Never use this function if the time the address space is pinned is
* not bounded.
*/
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
Acked-by: Michal Hocko <mhocko@...e.com>
> ---
> arch/arc/kernel/smp.c | 2 +-
> arch/blackfin/mach-common/smp.c | 2 +-
> arch/frv/mm/mmu-context.c | 2 +-
> arch/metag/kernel/smp.c | 2 +-
> arch/sh/kernel/smp.c | 2 +-
> arch/xtensa/kernel/smp.c | 2 +-
> include/linux/sched.h | 5 +++++
> kernel/fork.c | 4 ++--
> mm/swapfile.c | 10 +++++-----
> virt/kvm/async_pf.c | 2 +-
> 10 files changed, 19 insertions(+), 14 deletions(-)
>
> diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
> index 9cbc7aba3ede..eec70cb71db1 100644
> --- a/arch/arc/kernel/smp.c
> +++ b/arch/arc/kernel/smp.c
> @@ -124,7 +124,7 @@ void start_kernel_secondary(void)
> /* MMU, Caches, Vector Table, Interrupts etc */
> setup_processor();
>
> - atomic_inc(&mm->mm_users);
> + mmget(mm);
> mmgrab(mm);
> current->active_mm = mm;
> cpumask_set_cpu(cpu, mm_cpumask(mm));
> diff --git a/arch/blackfin/mach-common/smp.c b/arch/blackfin/mach-common/smp.c
> index bc5617ef7128..a2e6db2ce811 100644
> --- a/arch/blackfin/mach-common/smp.c
> +++ b/arch/blackfin/mach-common/smp.c
> @@ -307,7 +307,7 @@ void secondary_start_kernel(void)
> local_irq_disable();
>
> /* Attach the new idle task to the global mm. */
> - atomic_inc(&mm->mm_users);
> + mmget(mm);
> mmgrab(mm);
> current->active_mm = mm;
>
> diff --git a/arch/frv/mm/mmu-context.c b/arch/frv/mm/mmu-context.c
> index 81757d55a5b5..3473bde77f56 100644
> --- a/arch/frv/mm/mmu-context.c
> +++ b/arch/frv/mm/mmu-context.c
> @@ -188,7 +188,7 @@ int cxn_pin_by_pid(pid_t pid)
> task_lock(tsk);
> if (tsk->mm) {
> mm = tsk->mm;
> - atomic_inc(&mm->mm_users);
> + mmget(mm);
> ret = 0;
> }
> task_unlock(tsk);
> diff --git a/arch/metag/kernel/smp.c b/arch/metag/kernel/smp.c
> index af9cff547a19..c622293254e4 100644
> --- a/arch/metag/kernel/smp.c
> +++ b/arch/metag/kernel/smp.c
> @@ -344,7 +344,7 @@ asmlinkage void secondary_start_kernel(void)
> * All kernel threads share the same mm context; grab a
> * reference and switch to it.
> */
> - atomic_inc(&mm->mm_users);
> + mmget(mm);
> mmgrab(mm);
> current->active_mm = mm;
> cpumask_set_cpu(cpu, mm_cpumask(mm));
> diff --git a/arch/sh/kernel/smp.c b/arch/sh/kernel/smp.c
> index ee379c699c08..edc4769b047e 100644
> --- a/arch/sh/kernel/smp.c
> +++ b/arch/sh/kernel/smp.c
> @@ -179,7 +179,7 @@ asmlinkage void start_secondary(void)
>
> enable_mmu();
> mmgrab(mm);
> - atomic_inc(&mm->mm_users);
> + mmget(mm);
> current->active_mm = mm;
> #ifdef CONFIG_MMU
> enter_lazy_tlb(mm, current);
> diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c
> index 9bf5cea3bae4..fcea72019df7 100644
> --- a/arch/xtensa/kernel/smp.c
> +++ b/arch/xtensa/kernel/smp.c
> @@ -135,7 +135,7 @@ void secondary_start_kernel(void)
>
> /* All kernel threads share the same mm context. */
>
> - atomic_inc(&mm->mm_users);
> + mmget(mm);
> mmgrab(mm);
> current->active_mm = mm;
> cpumask_set_cpu(cpu, mm_cpumask(mm));
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 31ae1f49eebb..2ca3e15dad3b 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2899,6 +2899,11 @@ static inline void mmdrop_async(struct mm_struct *mm)
> }
> }
>
> +static inline void mmget(struct mm_struct *mm)
> +{
> + atomic_inc(&mm->mm_users);
> +}
> +
> static inline bool mmget_not_zero(struct mm_struct *mm)
> {
> return atomic_inc_not_zero(&mm->mm_users);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 997ac1d584f7..f9c32dc6ccbc 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -989,7 +989,7 @@ struct mm_struct *get_task_mm(struct task_struct *task)
> if (task->flags & PF_KTHREAD)
> mm = NULL;
> else
> - atomic_inc(&mm->mm_users);
> + mmget(mm);
> }
> task_unlock(task);
> return mm;
> @@ -1177,7 +1177,7 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
> vmacache_flush(tsk);
>
> if (clone_flags & CLONE_VM) {
> - atomic_inc(&oldmm->mm_users);
> + mmget(oldmm);
> mm = oldmm;
> goto good_mm;
> }
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index f30438970cd1..cf73169ce153 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1402,7 +1402,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
> * that.
> */
> start_mm = &init_mm;
> - atomic_inc(&init_mm.mm_users);
> + mmget(&init_mm);
>
> /*
> * Keep on scanning until all entries have gone. Usually,
> @@ -1451,7 +1451,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
> if (atomic_read(&start_mm->mm_users) == 1) {
> mmput(start_mm);
> start_mm = &init_mm;
> - atomic_inc(&init_mm.mm_users);
> + mmget(&init_mm);
> }
>
> /*
> @@ -1488,8 +1488,8 @@ int try_to_unuse(unsigned int type, bool frontswap,
> struct mm_struct *prev_mm = start_mm;
> struct mm_struct *mm;
>
> - atomic_inc(&new_start_mm->mm_users);
> - atomic_inc(&prev_mm->mm_users);
> + mmget(new_start_mm);
> + mmget(prev_mm);
> spin_lock(&mmlist_lock);
> while (swap_count(*swap_map) && !retval &&
> (p = p->next) != &start_mm->mmlist) {
> @@ -1512,7 +1512,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
>
> if (set_start_mm && *swap_map < swcount) {
> mmput(new_start_mm);
> - atomic_inc(&mm->mm_users);
> + mmget(mm);
> new_start_mm = mm;
> set_start_mm = 0;
> }
> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> index efeceb0a222d..9ec9cef2b207 100644
> --- a/virt/kvm/async_pf.c
> +++ b/virt/kvm/async_pf.c
> @@ -200,7 +200,7 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, unsigned long hva,
> work->addr = hva;
> work->arch = *arch;
> work->mm = current->mm;
> - atomic_inc(&work->mm->mm_users);
> + mmget(work->mm);
> kvm_get_kvm(work->vcpu->kvm);
>
> /* this can't really happen otherwise gfn_to_pfn_async
> --
> 2.11.0.1.gaa10c3f
>
--
Michal Hocko
SUSE Labs
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