From: Hyeonggon Yoo <42.hyeyoo@gmail•com>
To: Suren Baghdasaryan <surenb@google•com>
Cc: michel@lespinasse•org, joelaf@google•com, songliubraving@fb•com,
mhocko@suse•com, leewalsh@google•com, david@redhat•com,
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Subject: Re: [PATCH v4 18/33] mm: write-lock VMAs before removing them from VMA tree
Date: Wed, 1 Mar 2023 07:56:36 +0000 [thread overview]
Message-ID: <Y/8FNM9czzPHb5eG@localhost> (raw)
In-Reply-To: <Y/8CJQGNuMUTdLwP@localhost>
On Wed, Mar 01, 2023 at 07:43:33AM +0000, Hyeonggon Yoo wrote:
> On Mon, Feb 27, 2023 at 09:36:17AM -0800, Suren Baghdasaryan wrote:
> > Write-locking VMAs before isolating them ensures that page fault
> > handlers don't operate on isolated VMAs.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@google•com>
> > ---
> > mm/mmap.c | 1 +
> > mm/nommu.c | 5 +++++
> > 2 files changed, 6 insertions(+)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 1f42b9a52b9b..f7ed357056c4 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2255,6 +2255,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> > static inline int munmap_sidetree(struct vm_area_struct *vma,
> > struct ma_state *mas_detach)
> > {
> > + vma_start_write(vma);
> > mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
>
> I may be missing something, but have few questions:
>
> 1) Why does a writer need to both write-lock a VMA and mark the VMA detached
> when unmapping it, isn't it enough to just only write-lock a VMA?
>
> 2) as VMAs that are going to be removed are already locked in vma_prepare(),
> so I think this hunk could be dropped?
After sending this just realized that I did not consider simple munmap case :)
But I still think 1) and 3) are valid question.
>
> > if (mas_store_gfp(mas_detach, vma, GFP_KERNEL))
> > return -ENOMEM;
> > diff --git a/mm/nommu.c b/mm/nommu.c
> > index 57ba243c6a37..2ab162d773e2 100644
> > --- a/mm/nommu.c
> > +++ b/mm/nommu.c
> > @@ -588,6 +588,7 @@ static int delete_vma_from_mm(struct vm_area_struct *vma)
> > current->pid);
> > return -ENOMEM;
> > }
> > + vma_start_write(vma);
> > cleanup_vma_from_mm(vma);
>
> 3) I think this hunk could be dropped as Per-VMA lock depends on MMU anyway.
>
> Thanks,
> Hyeonggon
>
> >
> > /* remove from the MM's tree and list */
> > @@ -1519,6 +1520,10 @@ void exit_mmap(struct mm_struct *mm)
> > */
> > mmap_write_lock(mm);
> > for_each_vma(vmi, vma) {
> > + /*
> > + * No need to lock VMA because this is the only mm user and no
> > + * page fault handled can race with it.
> > + */
> > cleanup_vma_from_mm(vma);
> > delete_vma(mm, vma);
> > cond_resched();
> > --
> > 2.39.2.722.g9855ee24e9-goog
> >
> >
>
next prev parent reply other threads:[~2023-03-01 7:58 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-27 17:35 [PATCH v4 00/33] Per-VMA locks Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 01/33] maple_tree: Be more cautious about dead nodes Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 02/33] maple_tree: Detect dead nodes in mas_start() Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 03/33] maple_tree: Fix freeing of nodes in rcu mode Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 04/33] maple_tree: remove extra smp_wmb() from mas_dead_leaves() Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 05/33] maple_tree: Fix write memory barrier of nodes once dead for RCU mode Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 06/33] maple_tree: Add smp_rmb() to dead node detection Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 07/33] maple_tree: Add RCU lock checking to rcu callback functions Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 08/33] mm: Enable maple tree RCU mode by default Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 09/33] mm: introduce CONFIG_PER_VMA_LOCK Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 10/33] mm: rcu safe VMA freeing Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 11/33] mm: move mmap_lock assert function definitions Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 12/33] mm: add per-VMA lock and helper functions to control it Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 13/33] mm: mark VMA as being written when changing vm_flags Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 14/33] mm/mmap: move vma_prepare before vma_adjust_trans_huge Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 15/33] mm/khugepaged: write-lock VMA while collapsing a huge page Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 16/33] mm/mmap: write-lock VMAs in vma_prepare before modifying them Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 17/33] mm/mremap: write-lock VMA while remapping it to a new address range Suren Baghdasaryan
2023-03-01 7:01 ` Hyeonggon Yoo
2023-02-27 17:36 ` [PATCH v4 18/33] mm: write-lock VMAs before removing them from VMA tree Suren Baghdasaryan
2023-03-01 7:43 ` Hyeonggon Yoo
2023-03-01 7:56 ` Hyeonggon Yoo [this message]
2023-03-01 18:34 ` Suren Baghdasaryan
2023-03-01 18:42 ` Suren Baghdasaryan
2023-03-02 0:53 ` Hyeonggon Yoo
2023-03-02 2:21 ` Suren Baghdasaryan
2023-03-01 19:07 ` Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 19/33] mm: conditionally write-lock VMA in free_pgtables Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 20/33] kernel/fork: assert no VMA readers during its destruction Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 21/33] mm/mmap: prevent pagefault handler from racing with mmu_notifier registration Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 22/33] mm: introduce vma detached flag Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 23/33] mm: introduce lock_vma_under_rcu to be used from arch-specific code Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 24/33] mm: fall back to mmap_lock if vma->anon_vma is not yet set Suren Baghdasaryan
2023-03-01 9:54 ` Hyeonggon Yoo
2023-02-27 17:36 ` [PATCH v4 25/33] mm: add FAULT_FLAG_VMA_LOCK flag Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 26/33] mm: prevent do_swap_page from handling page faults under VMA lock Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 27/33] mm: prevent userfaults to be handled under per-vma lock Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 28/33] mm: introduce per-VMA lock statistics Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 29/33] x86/mm: try VMA lock-based page fault handling first Suren Baghdasaryan
2023-06-29 14:40 ` Jiri Slaby
2023-06-29 15:30 ` Suren Baghdasaryan
2023-06-30 6:35 ` Jiri Slaby
2023-06-30 8:28 ` Jiri Slaby
2023-06-30 8:43 ` Jiri Slaby
2023-06-30 17:40 ` Suren Baghdasaryan
2023-07-03 10:47 ` Jiri Slaby
2023-06-29 17:06 ` Linux regression tracking #adding (Thorsten Leemhuis)
2023-07-03 9:58 ` Linux regression tracking (Thorsten Leemhuis)
2023-02-27 17:36 ` [PATCH v4 30/33] arm64/mm: " Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 31/33] powerc/mm: " Suren Baghdasaryan
2023-03-06 15:42 ` [PATCH] powerpc/mm: fix mmap_lock bad unlock Laurent Dufour
2023-03-06 20:25 ` [PATCH v4 31/33] powerc/mm: try VMA lock-based page fault handling first Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 32/33] mm/mmap: free vm_area_struct without call_rcu in exit_mmap Suren Baghdasaryan
2023-02-27 17:36 ` [PATCH v4 33/33] mm: separate vma->lock from vm_area_struct Suren Baghdasaryan
2023-07-11 10:35 ` [PATCH v4 00/33] Per-VMA locks Leon Romanovsky
2023-07-11 10:39 ` Vlastimil Babka
2023-07-11 11:01 ` Leon Romanovsky
2023-07-11 11:09 ` Leon Romanovsky
2023-07-11 16:35 ` Suren Baghdasaryan
2023-07-11 17:14 ` Leon Romanovsky
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