Re: [PATCH v7 01/11] mm/mremap: Fix race between MOVE_PMD mremap and pageout
On Tue, 8 Jun 2021, Aneesh Kumar K.V wrote:
>
> mm/mremap: hold the rmap lock in write mode when moving page table
> entries.
>
> To avoid a race between rmap walk and mremap, mremap does
> take_rmap_locks().
> The lock was taken to ensure that rmap walk don't miss a page table entry
> due to
> PTE moves via move_pagetables(). The kernel does further optimization of
> this lock such that if we are going to find the newly added vma after the
> old vma, the rmap lock is not taken. This is because rmap walk would find
> the
> vmas in the same order and if we don't find the page table attached to
> older vma we would find it with the new vma which we would iterate later.
> The actual lifetime of the page is still controlled by the PTE lock.
>
> This patch updates the locking requirement to handle another race
> condition
> explained below with optimized mremap::
>
> Optmized PMD move
>
> CPU 1 CPU 2
> CPU 3
>
> mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
>
> mmap_write_lock_killable()
>
> addr = old_addr
> lock(pte_ptl)
> lock(pmd_ptl)
> pmd = *old_pmd
> pmd_clear(old_pmd)
> flush_tlb_range(old_addr)
>
> *new_pmd = pmd
>
> *new_addr = 10; and fills
>
> TLB with new addr
>
> and old pfn
>
> unlock(pmd_ptl)
> ptep_clear_flush()
> old pfn is free.
>
> Stale TLB entry
>
The PUD example below is mainly a waste a space and time:
"Optimized PUD move suffers from a similar race." would be better.
> Optmized PUD move:
>
> CPU 1 CPU 2
> CPU 3
>
> mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
>
> mmap_write_lock_killable()
>
> addr = old_addr
> lock(pte_ptl)
> lock(pud_ptl)
> pud = *old_pud
> pud_clear(old_pud)
> flush_tlb_range(old_addr)
>
> *new_pud = pud
>
> *new_addr = 10; and fills
>
> TLB with new addr
>
> and old pfn
>
> unlock(pud_ptl)
> ptep_clear_flush()
> old pfn is free.
>
> Stale TLB entry
>
> Both the above race condition can be fixed if we force mremap path to
> take rmap lock.
>
Don't forget the Fixes and Link you had in the previous version:
Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
Link:
https://lore.kernel.org/linux-mm/CAHk-=wgxvr04ebntxqfevontwnp6fdm+oj5vauqxp3s-huw...@mail.gmail.com
> Signed-off-by: Aneesh Kumar K.V
Thanks, this is orders of magnitude better!
Acked-by: Hugh Dickins
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 9cd352fb9cf8..f12df630fb37 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -517,7 +517,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
> } else if (IS_ENABLED(CONFIG_HAVE_MOVE_PUD) && extent ==
> PUD_SIZE) {
>
> if (move_pgt_entry(NORMAL_PUD, vma, old_addr, new_addr,
> -old_pud, new_pud, need_rmap_locks))
> +old_pud, new_pud, true))
> continue;
> }
>
> @@ -544,7 +544,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
>* moving at the PMD level if possible.
>*/
> if (move_pgt_entry(NORMAL_PMD, vma, old_addr, new_addr,
> -old_pmd, new_pmd, need_rmap_locks))
> +old_pmd, new_pmd, true))
> continue;
> }
>
>
Re: [PATCH v7 01/11] mm/mremap: Fix race between MOVE_PMD mremap and pageout
On Tue, Jun 08, 2021 at 04:47:19PM +0530, Aneesh Kumar K.V wrote:
> On 6/8/21 3:12 PM, Kirill A. Shutemov wrote:
> > On Tue, Jun 08, 2021 at 01:22:23PM +0530, Aneesh Kumar K.V wrote:
> > >
> > > Hi Hugh,
> > >
> > > Hugh Dickins writes:
> > >
> > > > On Mon, 7 Jun 2021, Aneesh Kumar K.V wrote:
> > > >
> > > > > CPU 1 CPU 2
> > > > > CPU 3
> > > > >
> > > > > mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
> > > > >
> > > > > mmap_write_lock_killable()
> > > > >
> > > > > addr = old_addr
> > > > > lock(pte_ptl)
> > > > > lock(pmd_ptl)
> > > > > pmd = *old_pmd
> > > > > pmd_clear(old_pmd)
> > > > > flush_tlb_range(old_addr)
> > > > >
> > > > > *new_pmd = pmd
> > > > >
> > > > > *new_addr = 10; and fills
> > > > >
> > > > > TLB with new addr
> > > > >
> > > > > and old pfn
> > > > >
> > > > > unlock(pmd_ptl)
> > > > > ptep_clear_flush()
> > > > > old pfn is free.
> > > > >
> > > > > Stale TLB entry
> > > > >
> > > > > Fix this race by holding pmd lock in pageout. This still doesn't
> > > > > handle the race
> > > > > between MOVE_PUD and pageout.
> > > > >
> > > > > Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
> > > > > Link:
> > > > > https://lore.kernel.org/linux-mm/CAHk-=wgxvr04ebntxqfevontwnp6fdm+oj5vauqxp3s-huw...@mail.gmail.com
> > > > > Signed-off-by: Aneesh Kumar K.V
> > > >
> > > > This seems very wrong to me, to require another level of locking in the
> > > > rmap lookup, just to fix some new pagetable games in mremap.
> > > >
> > > > But Linus asked "Am I missing something?": neither of you have mentioned
> > > > mremap's take_rmap_locks(), so I hope that already meets your need. And
> > > > if it needs to be called more often than before (see "need_rmap_locks"),
> > > > that's probably okay.
> > > >
> > > > Hugh
> > > >
> > >
> > > Thanks for reviewing the change. I missed the rmap lock in the code
> > > path. How about the below change?
> > >
> > > mm/mremap: hold the rmap lock in write mode when moving page table
> > > entries.
> > > To avoid a race between rmap walk and mremap, mremap does
> > > take_rmap_locks().
> > > The lock was taken to ensure that rmap walk don't miss a page table
> > > entry due to
> > > PTE moves via move_pagetables(). The kernel does further
> > > optimization of
> > > this lock such that if we are going to find the newly added vma
> > > after the
> > > old vma, the rmap lock is not taken. This is because rmap walk would
> > > find the
> > > vmas in the same order and if we don't find the page table attached
> > > to
> > > older vma we would find it with the new vma which we would iterate
> > > later.
> > > The actual lifetime of the page is still controlled by the PTE lock.
> > > This patch updates the locking requirement to handle another race
> > > condition
> > > explained below with optimized mremap::
> > > Optmized PMD move
> > > CPU 1 CPU 2
> > >CPU 3
> > > mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
> > > mmap_write_lock_killable()
> > > addr = old_addr
> > > lock(pte_ptl)
> > > lock(pmd_ptl)
> > > pmd = *old_pmd
> > > pmd_clear(old_pmd)
> > > flush_tlb_range(old_addr)
> > > *new_pmd = pmd
> > >
> > >*new_addr = 10; and fills
> > >
> > >TLB with new addr
> > >
> > >and old pfn
> > > unlock(pmd_ptl)
> > > ptep_clear_flush()
> > > old pfn is free.
> > >
> > >Stale TLB entry
> > > Optmized PUD move:
> > > CPU 1 CPU 2
> > >CPU 3
> > > mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
> > > mmap_write_lock_killable()
> > > addr = old_addr
> > > lock(pte_ptl)
> > > lock(pud_ptl)
> > > pud = *old_pud
> > > pud_clear(old_pud)
> >
Re: [PATCH v7 01/11] mm/mremap: Fix race between MOVE_PMD mremap and pageout
On 6/8/21 3:12 PM, Kirill A. Shutemov wrote:
On Tue, Jun 08, 2021 at 01:22:23PM +0530, Aneesh Kumar K.V wrote:
Hi Hugh,
Hugh Dickins writes:
On Mon, 7 Jun 2021, Aneesh Kumar K.V wrote:
CPU 1 CPU 2 CPU 3
mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
mmap_write_lock_killable()
addr = old_addr
lock(pte_ptl)
lock(pmd_ptl)
pmd = *old_pmd
pmd_clear(old_pmd)
flush_tlb_range(old_addr)
*new_pmd = pmd
*new_addr = 10; and fills
TLB
with new addr
and old
pfn
unlock(pmd_ptl)
ptep_clear_flush()
old pfn is free.
Stale
TLB entry
Fix this race by holding pmd lock in pageout. This still doesn't handle the race
between MOVE_PUD and pageout.
Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
Link:
https://lore.kernel.org/linux-mm/CAHk-=wgxvr04ebntxqfevontwnp6fdm+oj5vauqxp3s-huw...@mail.gmail.com
Signed-off-by: Aneesh Kumar K.V
This seems very wrong to me, to require another level of locking in the
rmap lookup, just to fix some new pagetable games in mremap.
But Linus asked "Am I missing something?": neither of you have mentioned
mremap's take_rmap_locks(), so I hope that already meets your need. And
if it needs to be called more often than before (see "need_rmap_locks"),
that's probably okay.
Hugh
Thanks for reviewing the change. I missed the rmap lock in the code
path. How about the below change?
mm/mremap: hold the rmap lock in write mode when moving page table entries.
To avoid a race between rmap walk and mremap, mremap does take_rmap_locks().
The lock was taken to ensure that rmap walk don't miss a page table entry
due to
PTE moves via move_pagetables(). The kernel does further optimization of
this lock such that if we are going to find the newly added vma after the
old vma, the rmap lock is not taken. This is because rmap walk would find
the
vmas in the same order and if we don't find the page table attached to
older vma we would find it with the new vma which we would iterate later.
The actual lifetime of the page is still controlled by the PTE lock.
This patch updates the locking requirement to handle another race condition
explained below with optimized mremap::
Optmized PMD move
CPU 1 CPU 2 CPU 3
mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
mmap_write_lock_killable()
addr = old_addr
lock(pte_ptl)
lock(pmd_ptl)
pmd = *old_pmd
pmd_clear(old_pmd)
flush_tlb_range(old_addr)
*new_pmd = pmd
*new_addr = 10; and fills
TLB with new addr
and old pfn
unlock(pmd_ptl)
ptep_clear_flush()
old pfn is free.
Stale TLB entry
Optmized PUD move:
CPU 1 CPU 2 CPU 3
mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
mmap_write_lock_killable()
addr = old_addr
lock(pte_ptl)
lock(pud_ptl)
pud = *old_pud
pud_clear(old_pud)
flush_tlb_range(old_addr)
*new_pud = pud
*new_addr = 10; and fills
TLB with new addr
and old pfn
unlock(pud_ptl)
ptep_clear_flush()
old pfn is free.
Stale TLB entry
Both the above race condition can be fixed if we force mremap path to take rmap lock.
Signed-off-by: Aneesh Kumar K.V
Looks like it should be enough to address the
Re: [PATCH v7 01/11] mm/mremap: Fix race between MOVE_PMD mremap and pageout
On Tue, Jun 08, 2021 at 01:22:23PM +0530, Aneesh Kumar K.V wrote:
>
> Hi Hugh,
>
> Hugh Dickins writes:
>
> > On Mon, 7 Jun 2021, Aneesh Kumar K.V wrote:
> >
> >> CPU 1 CPU 2
> >> CPU 3
> >>
> >> mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
> >>
> >> mmap_write_lock_killable()
> >>
> >>addr = old_addr
> >>lock(pte_ptl)
> >> lock(pmd_ptl)
> >> pmd = *old_pmd
> >> pmd_clear(old_pmd)
> >> flush_tlb_range(old_addr)
> >>
> >> *new_pmd = pmd
> >>
> >> *new_addr = 10; and fills
> >>TLB
> >> with new addr
> >>and old
> >> pfn
> >>
> >> unlock(pmd_ptl)
> >>ptep_clear_flush()
> >>old pfn is free.
> >>Stale
> >> TLB entry
> >>
> >> Fix this race by holding pmd lock in pageout. This still doesn't handle
> >> the race
> >> between MOVE_PUD and pageout.
> >>
> >> Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
> >> Link:
> >> https://lore.kernel.org/linux-mm/CAHk-=wgxvr04ebntxqfevontwnp6fdm+oj5vauqxp3s-huw...@mail.gmail.com
> >> Signed-off-by: Aneesh Kumar K.V
> >
> > This seems very wrong to me, to require another level of locking in the
> > rmap lookup, just to fix some new pagetable games in mremap.
> >
> > But Linus asked "Am I missing something?": neither of you have mentioned
> > mremap's take_rmap_locks(), so I hope that already meets your need. And
> > if it needs to be called more often than before (see "need_rmap_locks"),
> > that's probably okay.
> >
> > Hugh
> >
>
> Thanks for reviewing the change. I missed the rmap lock in the code
> path. How about the below change?
>
> mm/mremap: hold the rmap lock in write mode when moving page table
> entries.
>
> To avoid a race between rmap walk and mremap, mremap does
> take_rmap_locks().
> The lock was taken to ensure that rmap walk don't miss a page table entry
> due to
> PTE moves via move_pagetables(). The kernel does further optimization of
> this lock such that if we are going to find the newly added vma after the
> old vma, the rmap lock is not taken. This is because rmap walk would find
> the
> vmas in the same order and if we don't find the page table attached to
> older vma we would find it with the new vma which we would iterate later.
> The actual lifetime of the page is still controlled by the PTE lock.
>
> This patch updates the locking requirement to handle another race
> condition
> explained below with optimized mremap::
>
> Optmized PMD move
>
> CPU 1 CPU 2
> CPU 3
>
> mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
>
> mmap_write_lock_killable()
>
> addr = old_addr
> lock(pte_ptl)
> lock(pmd_ptl)
> pmd = *old_pmd
> pmd_clear(old_pmd)
> flush_tlb_range(old_addr)
>
> *new_pmd = pmd
>
> *new_addr = 10; and fills
>
> TLB with new addr
>
> and old pfn
>
> unlock(pmd_ptl)
> ptep_clear_flush()
> old pfn is free.
>
> Stale TLB entry
>
> Optmized PUD move:
>
> CPU 1 CPU 2
> CPU 3
>
> mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
>
> mmap_write_lock_killable()
>
> addr = old_addr
> lock(pte_ptl)
> lock(pud_ptl)
> pud = *old_pud
> pud_clear(old_pud)
> flush_tlb_range(old_addr)
>
> *new_pud = pud
>
> *new_addr = 10; and fills
>
> TLB with new addr
>
> and old pfn
>
> unlock(pud_ptl)
> ptep_clear_flush()
> old pfn is free.
>
Re: [PATCH v7 01/11] mm/mremap: Fix race between MOVE_PMD mremap and pageout
Hi Hugh,
Hugh Dickins writes:
> On Mon, 7 Jun 2021, Aneesh Kumar K.V wrote:
>
>> CPU 1CPU 2
>> CPU 3
>>
>> mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
>>
>> mmap_write_lock_killable()
>>
>> addr = old_addr
>> lock(pte_ptl)
>> lock(pmd_ptl)
>> pmd = *old_pmd
>> pmd_clear(old_pmd)
>> flush_tlb_range(old_addr)
>>
>> *new_pmd = pmd
>>
>> *new_addr = 10; and fills
>> TLB
>> with new addr
>> and old
>> pfn
>>
>> unlock(pmd_ptl)
>> ptep_clear_flush()
>> old pfn is free.
>> Stale
>> TLB entry
>>
>> Fix this race by holding pmd lock in pageout. This still doesn't handle the
>> race
>> between MOVE_PUD and pageout.
>>
>> Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
>> Link:
>> https://lore.kernel.org/linux-mm/CAHk-=wgxvr04ebntxqfevontwnp6fdm+oj5vauqxp3s-huw...@mail.gmail.com
>> Signed-off-by: Aneesh Kumar K.V
>
> This seems very wrong to me, to require another level of locking in the
> rmap lookup, just to fix some new pagetable games in mremap.
>
> But Linus asked "Am I missing something?": neither of you have mentioned
> mremap's take_rmap_locks(), so I hope that already meets your need. And
> if it needs to be called more often than before (see "need_rmap_locks"),
> that's probably okay.
>
> Hugh
>
Thanks for reviewing the change. I missed the rmap lock in the code
path. How about the below change?
mm/mremap: hold the rmap lock in write mode when moving page table entries.
To avoid a race between rmap walk and mremap, mremap does take_rmap_locks().
The lock was taken to ensure that rmap walk don't miss a page table entry
due to
PTE moves via move_pagetables(). The kernel does further optimization of
this lock such that if we are going to find the newly added vma after the
old vma, the rmap lock is not taken. This is because rmap walk would find
the
vmas in the same order and if we don't find the page table attached to
older vma we would find it with the new vma which we would iterate later.
The actual lifetime of the page is still controlled by the PTE lock.
This patch updates the locking requirement to handle another race condition
explained below with optimized mremap::
Optmized PMD move
CPU 1 CPU 2
CPU 3
mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
mmap_write_lock_killable()
addr = old_addr
lock(pte_ptl)
lock(pmd_ptl)
pmd = *old_pmd
pmd_clear(old_pmd)
flush_tlb_range(old_addr)
*new_pmd = pmd
*new_addr = 10; and fills
TLB with new addr
and old pfn
unlock(pmd_ptl)
ptep_clear_flush()
old pfn is free.
Stale TLB entry
Optmized PUD move:
CPU 1 CPU 2
CPU 3
mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
mmap_write_lock_killable()
addr = old_addr
lock(pte_ptl)
lock(pud_ptl)
pud = *old_pud
pud_clear(old_pud)
flush_tlb_range(old_addr)
*new_pud = pud
*new_addr = 10; and fills
TLB with new addr
and old pfn
unlock(pud_ptl)
ptep_clear_flush()
old pfn is free.
Stale TLB entry
Both the above race condition can be fixed if we force mremap path to take
rmap lock.
Signed-off-by: Aneesh Kumar K.V
diff --git a/mm/mremap.c b/mm/mremap.c
index 9cd352fb9cf8..f12df630fb37 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -517,7
Re: [PATCH v7 01/11] mm/mremap: Fix race between MOVE_PMD mremap and pageout
On Mon, 7 Jun 2021, Aneesh Kumar K.V wrote:
> CPU 1 CPU 2 CPU 3
>
> mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
>
> mmap_write_lock_killable()
>
> addr = old_addr
> lock(pte_ptl)
> lock(pmd_ptl)
> pmd = *old_pmd
> pmd_clear(old_pmd)
> flush_tlb_range(old_addr)
>
> *new_pmd = pmd
>
> *new_addr = 10; and fills
> TLB
> with new addr
> and old
> pfn
>
> unlock(pmd_ptl)
> ptep_clear_flush()
> old pfn is free.
> Stale
> TLB entry
>
> Fix this race by holding pmd lock in pageout. This still doesn't handle the
> race
> between MOVE_PUD and pageout.
>
> Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
> Link:
> https://lore.kernel.org/linux-mm/CAHk-=wgxvr04ebntxqfevontwnp6fdm+oj5vauqxp3s-huw...@mail.gmail.com
> Signed-off-by: Aneesh Kumar K.V
This seems very wrong to me, to require another level of locking in the
rmap lookup, just to fix some new pagetable games in mremap.
But Linus asked "Am I missing something?": neither of you have mentioned
mremap's take_rmap_locks(), so I hope that already meets your need. And
if it needs to be called more often than before (see "need_rmap_locks"),
that's probably okay.
Hugh
> ---
> include/linux/rmap.h | 9 ++---
> mm/page_vma_mapped.c | 36 ++--
> 2 files changed, 24 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index def5c62c93b3..272ab0c2b60b 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -207,7 +207,8 @@ struct page_vma_mapped_walk {
> unsigned long address;
> pmd_t *pmd;
> pte_t *pte;
> - spinlock_t *ptl;
> + spinlock_t *pte_ptl;
> + spinlock_t *pmd_ptl;
> unsigned int flags;
> };
>
> @@ -216,8 +217,10 @@ static inline void page_vma_mapped_walk_done(struct
> page_vma_mapped_walk *pvmw)
> /* HugeTLB pte is set to the relevant page table entry without
> pte_mapped. */
> if (pvmw->pte && !PageHuge(pvmw->page))
> pte_unmap(pvmw->pte);
> - if (pvmw->ptl)
> - spin_unlock(pvmw->ptl);
> + if (pvmw->pte_ptl)
> + spin_unlock(pvmw->pte_ptl);
> + if (pvmw->pmd_ptl)
> + spin_unlock(pvmw->pmd_ptl);
> }
>
> bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index 2cf01d933f13..87a2c94c7e27 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -47,8 +47,10 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw)
> return false;
> }
> }
> - pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
> - spin_lock(pvmw->ptl);
> + if (USE_SPLIT_PTE_PTLOCKS) {
> + pvmw->pte_ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
> + spin_lock(pvmw->pte_ptl);
> + }
> return true;
> }
>
> @@ -162,8 +164,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk
> *pvmw)
> if (!pvmw->pte)
> return false;
>
> - pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
> - spin_lock(pvmw->ptl);
> + pvmw->pte_ptl = huge_pte_lockptr(page_hstate(page), mm,
> pvmw->pte);
> + spin_lock(pvmw->pte_ptl);
> if (!check_pte(pvmw))
> return not_found(pvmw);
> return true;
> @@ -179,6 +181,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk
> *pvmw)
> if (!pud_present(*pud))
> return false;
> pvmw->pmd = pmd_offset(pud, pvmw->address);
> + pvmw->pmd_ptl = pmd_lock(mm, pvmw->pmd);
> /*
>* Make sure the pmd value isn't cached in a register by the
>* compiler and used as a stale value after we've observed a
> @@ -186,7 +189,6 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk
> *pvmw)
>*/
> pmde = READ_ONCE(*pvmw->pmd);
> if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
> - pvmw->ptl = pmd_lock(mm, pvmw->pmd);
> if (likely(pmd_trans_huge(*pvmw->pmd))) {
> if (pvmw->flags & PVMW_MIGRATION)
> return not_found(pvmw);
> @@ -206,14 +208,10 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk
> *pvmw)
> }
> }
> return not_found(pvmw);
> - } else {
> - /* THP pmd was split under us: handle on
[PATCH v7 01/11] mm/mremap: Fix race between MOVE_PMD mremap and pageout
CPU 1 CPU 2 CPU 3
mremap(old_addr, new_addr) page_shrinker/try_to_unmap_one
mmap_write_lock_killable()
addr = old_addr
lock(pte_ptl)
lock(pmd_ptl)
pmd = *old_pmd
pmd_clear(old_pmd)
flush_tlb_range(old_addr)
*new_pmd = pmd
*new_addr = 10; and fills
TLB
with new addr
and old
pfn
unlock(pmd_ptl)
ptep_clear_flush()
old pfn is free.
Stale
TLB entry
Fix this race by holding pmd lock in pageout. This still doesn't handle the race
between MOVE_PUD and pageout.
Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
Link:
https://lore.kernel.org/linux-mm/CAHk-=wgxvr04ebntxqfevontwnp6fdm+oj5vauqxp3s-huw...@mail.gmail.com
Signed-off-by: Aneesh Kumar K.V
---
include/linux/rmap.h | 9 ++---
mm/page_vma_mapped.c | 36 ++--
2 files changed, 24 insertions(+), 21 deletions(-)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index def5c62c93b3..272ab0c2b60b 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -207,7 +207,8 @@ struct page_vma_mapped_walk {
unsigned long address;
pmd_t *pmd;
pte_t *pte;
- spinlock_t *ptl;
+ spinlock_t *pte_ptl;
+ spinlock_t *pmd_ptl;
unsigned int flags;
};
@@ -216,8 +217,10 @@ static inline void page_vma_mapped_walk_done(struct
page_vma_mapped_walk *pvmw)
/* HugeTLB pte is set to the relevant page table entry without
pte_mapped. */
if (pvmw->pte && !PageHuge(pvmw->page))
pte_unmap(pvmw->pte);
- if (pvmw->ptl)
- spin_unlock(pvmw->ptl);
+ if (pvmw->pte_ptl)
+ spin_unlock(pvmw->pte_ptl);
+ if (pvmw->pmd_ptl)
+ spin_unlock(pvmw->pmd_ptl);
}
bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw);
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 2cf01d933f13..87a2c94c7e27 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -47,8 +47,10 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw)
return false;
}
}
- pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
- spin_lock(pvmw->ptl);
+ if (USE_SPLIT_PTE_PTLOCKS) {
+ pvmw->pte_ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
+ spin_lock(pvmw->pte_ptl);
+ }
return true;
}
@@ -162,8 +164,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
if (!pvmw->pte)
return false;
- pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
- spin_lock(pvmw->ptl);
+ pvmw->pte_ptl = huge_pte_lockptr(page_hstate(page), mm,
pvmw->pte);
+ spin_lock(pvmw->pte_ptl);
if (!check_pte(pvmw))
return not_found(pvmw);
return true;
@@ -179,6 +181,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
if (!pud_present(*pud))
return false;
pvmw->pmd = pmd_offset(pud, pvmw->address);
+ pvmw->pmd_ptl = pmd_lock(mm, pvmw->pmd);
/*
* Make sure the pmd value isn't cached in a register by the
* compiler and used as a stale value after we've observed a
@@ -186,7 +189,6 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
*/
pmde = READ_ONCE(*pvmw->pmd);
if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
- pvmw->ptl = pmd_lock(mm, pvmw->pmd);
if (likely(pmd_trans_huge(*pvmw->pmd))) {
if (pvmw->flags & PVMW_MIGRATION)
return not_found(pvmw);
@@ -206,14 +208,10 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk
*pvmw)
}
}
return not_found(pvmw);
- } else {
- /* THP pmd was split under us: handle on pte level */
- spin_unlock(pvmw->ptl);
- pvmw->ptl = NULL;
}
- } else if (!pmd_present(pmde)) {
- return false;
- }
+ } else if (!pmd_present(pmde))
+ return not_found(pvmw);
+
if (!map_pte(pvmw))
goto next_pte;
while (1) {
@@ -233,19 +231,21 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk
*pvmw)
/* Did we cross page table boundary? */
if (pvmw->address %
