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Date: Fri, 28 May 2021 17:42:28 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Liam Howlett <liam.howlett@...cle.com>
Cc: "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Song Liu <songliubraving@...com>,
Davidlohr Bueso <dave@...olabs.net>,
"Paul E . McKenney" <paulmck@...nel.org>,
Matthew Wilcox <willy@...radead.org>,
Laurent Dufour <ldufour@...ux.ibm.com>,
David Rientjes <rientjes@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>,
Rik van Riel <riel@...riel.com>,
Peter Zijlstra <peterz@...radead.org>,
Michel Lespinasse <walken.cr@...il.com>
Subject: Re: [PATCH 32/94] kernel/fork: Convert dup_mmap to use maple tree
On Wed, Apr 28, 2021 at 8:36 AM Liam Howlett <liam.howlett@...cle.com> wrote:
>
> Use the maple tree iterator to duplicate the mm_struct trees.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> ---
> include/linux/mm.h | 2 --
> include/linux/sched/mm.h | 3 +++
> kernel/fork.c | 24 +++++++++++++++++++-----
> mm/mmap.c | 4 ----
> 4 files changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e89bacfa9145..7f7dff6ad884 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2498,8 +2498,6 @@ extern bool arch_has_descending_max_zone_pfns(void);
> /* nommu.c */
> extern atomic_long_t mmap_pages_allocated;
> extern int nommu_shrink_inode_mappings(struct inode *, size_t, size_t);
> -/* maple_tree */
> -void vma_store(struct mm_struct *mm, struct vm_area_struct *vma);
>
> /* interval_tree.c */
> void vma_interval_tree_insert(struct vm_area_struct *node,
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index e24b1fe348e3..76cab3aea6ab 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -8,6 +8,7 @@
> #include <linux/mm_types.h>
> #include <linux/gfp.h>
> #include <linux/sync_core.h>
> +#include <linux/maple_tree.h>
>
> /*
> * Routines for handling mm_structs
> @@ -67,11 +68,13 @@ static inline void mmdrop(struct mm_struct *mm)
> */
> static inline void mmget(struct mm_struct *mm)
> {
> + mt_set_in_rcu(&mm->mm_mt);
> atomic_inc(&mm->mm_users);
> }
>
> static inline bool mmget_not_zero(struct mm_struct *mm)
> {
> + mt_set_in_rcu(&mm->mm_mt);
Should you be calling mt_set_in_rcu() if atomic_inc_not_zero() failed?
I don't think mmput() is called after mmget_not_zero() fails and
mt_clear_in_rcu() will not be called.
> return atomic_inc_not_zero(&mm->mm_users);
> }
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index c37abaf28eb9..832416ff613e 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -477,7 +477,9 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
> struct rb_node **rb_link, *rb_parent;
> int retval;
> - unsigned long charge;
> + unsigned long charge = 0;
> + MA_STATE(old_mas, &oldmm->mm_mt, 0, 0);
> + MA_STATE(mas, &mm->mm_mt, 0, 0);
> LIST_HEAD(uf);
>
> uprobe_start_dup_mmap();
> @@ -511,7 +513,13 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> goto out;
>
> prev = NULL;
> - for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
> +
> + retval = mas_entry_count(&mas, oldmm->map_count);
> + if (retval)
> + goto fail_nomem;
> +
> + rcu_read_lock();
> + mas_for_each(&old_mas, mpnt, ULONG_MAX) {
> struct file *file;
>
> if (mpnt->vm_flags & VM_DONTCOPY) {
> @@ -525,7 +533,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> */
> if (fatal_signal_pending(current)) {
> retval = -EINTR;
> - goto out;
> + goto loop_out;
> }
> if (mpnt->vm_flags & VM_ACCOUNT) {
> unsigned long len = vma_pages(mpnt);
> @@ -594,7 +602,9 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> rb_parent = &tmp->vm_rb;
>
> /* Link the vma into the MT */
> - vma_store(mm, tmp);
> + mas.index = tmp->vm_start;
> + mas.last = tmp->vm_end - 1;
> + mas_store(&mas, tmp);
>
> mm->map_count++;
> if (!(tmp->vm_flags & VM_WIPEONFORK))
> @@ -604,14 +614,17 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> tmp->vm_ops->open(tmp);
>
> if (retval)
> - goto out;
> + goto loop_out;
> }
> /* a new mm has just been created */
> retval = arch_dup_mmap(oldmm, mm);
> +loop_out:
> out:
> + rcu_read_unlock();
> mmap_write_unlock(mm);
> flush_tlb_mm(oldmm);
> mmap_write_unlock(oldmm);
> + mas_destroy(&mas);
> dup_userfaultfd_complete(&uf);
> fail_uprobe_end:
> uprobe_end_dup_mmap();
> @@ -1092,6 +1105,7 @@ static inline void __mmput(struct mm_struct *mm)
> {
> VM_BUG_ON(atomic_read(&mm->mm_users));
>
> + mt_clear_in_rcu(&mm->mm_mt);
> uprobe_clear_state(mm);
> exit_aio(mm);
> ksm_exit(mm);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 929c2f9eb3f5..1bd43f4db28e 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -780,10 +780,6 @@ static inline void vma_mt_store(struct mm_struct *mm, struct vm_area_struct *vma
> GFP_KERNEL);
> }
>
> -void vma_store(struct mm_struct *mm, struct vm_area_struct *vma) {
> - vma_mt_store(mm, vma);
> -}
> -
> static void
> __vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
> struct vm_area_struct *prev, struct rb_node **rb_link,
> --
> 2.30.2
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