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Date: Thu, 19 Jun 2014 20:15:43 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Vladimir Davydov <vdavydov@...allels.com>,
Andi Kleen <andi@...stfloor.org>
Cc: akpm@...ux-foundation.org, rientjes@...gle.com, cl@...ux.com,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] fork/exec: cleanup mm initialization
On 06/19, Vladimir Davydov wrote:
>
> mm initialization on fork/exec is spread all over the place, which makes
> the code look inconsistent.
>
> We have mm_init(), which is supposed to init/nullify mm's internals, but
> it doesn't init all the fields it should:
>
> - on fork ->mmap,mm_rb,vmacache_seqnum,map_count,mm_cpumask,locked_vm
> are zeroed in dup_mmap();
>
> - on fork ->pmd_huge_pte is zeroed in dup_mm(), immediately before
> calling mm_init();
>
> - ->cpu_vm_mask_var ptr is initialized by mm_init_cpumask(), which is
> called before mm_init() on both fork and exec;
>
> - ->context is initialized by init_new_context(), which is called after
> mm_init() on both fork and exec;
>
> Let's consolidate all the initializations in mm_init() to make the code
> look cleaner.
Yes, agreed. Afaics, the patch is fine (2 and 3 too).
This is off-topic, but why init_new_context() copies ldt even on exec?
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
> ---
> fs/exec.c | 4 ----
> include/linux/mm_types.h | 1 +
> kernel/fork.c | 47 ++++++++++++++++++++--------------------------
> 3 files changed, 21 insertions(+), 31 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index a3d33fe592d6..2ef2751f5a8d 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -368,10 +368,6 @@ static int bprm_mm_init(struct linux_binprm *bprm)
> if (!mm)
> goto err;
>
> - err = init_new_context(current, mm);
> - if (err)
> - goto err;
> -
> err = __bprm_mm_init(bprm);
> if (err)
> goto err;
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 96c5750e3110..21bff4be4379 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -461,6 +461,7 @@ static inline void mm_init_cpumask(struct mm_struct *mm)
> #ifdef CONFIG_CPUMASK_OFFSTACK
> mm->cpu_vm_mask_var = &mm->cpumask_allocation;
> #endif
> + cpumask_clear(mm->cpu_vm_mask_var);
> }
>
> /* Future-safe accessor for struct mm_struct's cpu_vm_mask. */
> diff --git a/kernel/fork.c b/kernel/fork.c
> index d2799d1fc952..01f0d0c56cb9 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -365,12 +365,6 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
> */
> down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
>
> - mm->locked_vm = 0;
> - mm->mmap = NULL;
> - mm->vmacache_seqnum = 0;
> - mm->map_count = 0;
> - cpumask_clear(mm_cpumask(mm));
> - mm->mm_rb = RB_ROOT;
> rb_link = &mm->mm_rb.rb_node;
> rb_parent = NULL;
> pprev = &mm->mmap;
> @@ -529,17 +523,27 @@ static void mm_init_aio(struct mm_struct *mm)
>
> static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
> {
> + mm->mmap = NULL;
> + mm->mm_rb = RB_ROOT;
> + mm->vmacache_seqnum = 0;
> atomic_set(&mm->mm_users, 1);
> atomic_set(&mm->mm_count, 1);
> init_rwsem(&mm->mmap_sem);
> INIT_LIST_HEAD(&mm->mmlist);
> mm->core_state = NULL;
> atomic_long_set(&mm->nr_ptes, 0);
> + mm->map_count = 0;
> + mm->locked_vm = 0;
> memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
> spin_lock_init(&mm->page_table_lock);
> + mm_init_cpumask(mm);
> mm_init_aio(mm);
> mm_init_owner(mm, p);
> + mmu_notifier_mm_init(mm);
> clear_tlb_flush_pending(mm);
> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
> + mm->pmd_huge_pte = NULL;
> +#endif
>
> if (current->mm) {
> mm->flags = current->mm->flags & MMF_INIT_MASK;
> @@ -549,11 +553,17 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
> mm->def_flags = 0;
> }
>
> - if (likely(!mm_alloc_pgd(mm))) {
> - mmu_notifier_mm_init(mm);
> - return mm;
> - }
> + if (mm_alloc_pgd(mm))
> + goto fail_nopgd;
> +
> + if (init_new_context(p, mm))
> + goto fail_nocontext;
>
> + return mm;
> +
> +fail_nocontext:
> + mm_free_pgd(mm);
> +fail_nopgd:
> free_mm(mm);
> return NULL;
> }
> @@ -587,7 +597,6 @@ struct mm_struct *mm_alloc(void)
> return NULL;
>
> memset(mm, 0, sizeof(*mm));
> - mm_init_cpumask(mm);
> return mm_init(mm, current);
> }
>
> @@ -819,17 +828,10 @@ static struct mm_struct *dup_mm(struct task_struct *tsk)
> goto fail_nomem;
>
> memcpy(mm, oldmm, sizeof(*mm));
> - mm_init_cpumask(mm);
>
> -#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
> - mm->pmd_huge_pte = NULL;
> -#endif
> if (!mm_init(mm, tsk))
> goto fail_nomem;
>
> - if (init_new_context(tsk, mm))
> - goto fail_nocontext;
> -
> dup_mm_exe_file(oldmm, mm);
>
> err = dup_mmap(mm, oldmm);
> @@ -851,15 +853,6 @@ free_pt:
>
> fail_nomem:
> return NULL;
> -
> -fail_nocontext:
> - /*
> - * If init_new_context() failed, we cannot use mmput() to free the mm
> - * because it calls destroy_context()
> - */
> - mm_free_pgd(mm);
> - free_mm(mm);
> - return NULL;
> }
>
> static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
> --
> 1.7.10.4
>
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