This collection of patches add the missing overflow checks in arch-specific gup.c variants for x86 and s390. Those were missed in backport of 8fde12ca79af ("mm: prevent get_user_pages() from overflowing page refcount") as mainline had a single gup.c implementation at that point. See individual patches for details. Vlastimil -- 2.24.0
The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from overflowing page refcount") was backported to 4.9.y stable as commit 2ed768cfd895. The backport however missed that in 4.9, there are several arch-specific gup.c versions with fast gup implementations, so these do not prevent refcount overflow. This is partially fixed for x86 in stable-only commit d73af79742e7 ("x86, mm, gup: prevent get_page() race with munmap in paravirt guest"). This stable-only commit adds missing parts to x86 version, as well as s390 version, both taken from the SUSE SLES/openSUSE 4.12-based kernels. The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely the known overflow scenario based on FUSE, which needs 140GB of RAM, is a problem for those architectures, and I don't feel confident enough to patch them. Signed-off-by: Vlastimil Babka <vbabka@suse.cz> --- arch/s390/mm/gup.c | 9 ++++++--- arch/x86/mm/gup.c | 10 ++++++++-- 2 files changed, 14 insertions(+), 5 deletions(-) diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c index 97fc449a7470..33a940389a6d 100644 --- a/arch/s390/mm/gup.c +++ b/arch/s390/mm/gup.c @@ -38,7 +38,8 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte); head = compound_head(page); - if (!page_cache_get_speculative(head)) + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_get_speculative(head))) return 0; if (unlikely(pte_val(pte) != pte_val(*ptep))) { put_page(head); @@ -76,7 +77,8 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - if (!page_cache_add_speculative(head, refs)) { + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_add_speculative(head, refs))) { *nr -= refs; return 0; } @@ -150,7 +152,8 @@ static int gup_huge_pud(pud_t *pudp, pud_t pud, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - if (!page_cache_add_speculative(head, refs)) { + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_add_speculative(head, refs))) { *nr -= refs; return 0; } diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index d7db45bdfb3b..551fc7fea046 100644 --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -202,10 +202,12 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr, undo_dev_pagemap(nr, nr_start, pages); return 0; } + if (unlikely(!try_get_page(page))) { + put_dev_pagemap(pgmap); + return 0; + } SetPageReferenced(page); pages[*nr] = page; - get_page(page); - put_dev_pagemap(pgmap); (*nr)++; pfn++; } while (addr += PAGE_SIZE, addr != end); @@ -230,6 +232,8 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr, refs = 0; head = pmd_page(pmd); + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) + return 0; page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); do { VM_BUG_ON_PAGE(compound_head(page) != head, page); @@ -289,6 +293,8 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr, refs = 0; head = pud_page(pud); + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) + return 0; page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); do { VM_BUG_ON_PAGE(compound_head(page) != head, page); -- 2.24.0
The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from overflowing page refcount") was backported to 4.14.y stable as commit 04198de24771. The backport however missed that in 4.14, there are several arch-specific gup.c versions with fast gup implementations, so these do not prevent refcount overflow. This stable-only commit fixes the s390 version, and is based on the backport in SUSE SLES/openSUSE 4.12-based kernels. The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely the known overflow scenario based on FUSE, which needs 140GB of RAM, is a problem for those architectures, and I don't feel confident enough to patch them. Signed-off-by: Vlastimil Babka <vbabka@suse.cz> --- arch/s390/mm/gup.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c index 05c8abd864f1..9bce54eac0b0 100644 --- a/arch/s390/mm/gup.c +++ b/arch/s390/mm/gup.c @@ -39,7 +39,8 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte); head = compound_head(page); - if (!page_cache_get_speculative(head)) + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_get_speculative(head))) return 0; if (unlikely(pte_val(pte) != pte_val(*ptep))) { put_page(head); @@ -77,7 +78,8 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - if (!page_cache_add_speculative(head, refs)) { + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_add_speculative(head, refs))) { *nr -= refs; return 0; } @@ -151,7 +153,8 @@ static int gup_huge_pud(pud_t *pudp, pud_t pud, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - if (!page_cache_add_speculative(head, refs)) { + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_add_speculative(head, refs))) { *nr -= refs; return 0; } -- 2.24.0
The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from overflowing page refcount") was backported to 4.19.y stable as commit d972ebbf42ba. The backport however missed that in 4.19, there are several arch-specific gup.c versions with fast gup implementations, so these do not prevent refcount overflow. This stable-only commit fixes the s390 version, and is based on the backport in SUSE SLES/openSUSE 4.12-based kernels. The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely the known overflow scenario based on FUSE, which needs 140GB of RAM, is a problem for those architectures, and I don't feel confident enough to patch them. Signed-off-by: Vlastimil Babka <vbabka@suse.cz> --- arch/s390/mm/gup.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c index 2809d11c7a28..9b5b866d8adf 100644 --- a/arch/s390/mm/gup.c +++ b/arch/s390/mm/gup.c @@ -39,7 +39,8 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte); head = compound_head(page); - if (!page_cache_get_speculative(head)) + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_get_speculative(head))) return 0; if (unlikely(pte_val(pte) != pte_val(*ptep))) { put_page(head); @@ -77,7 +78,8 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - if (!page_cache_add_speculative(head, refs)) { + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_add_speculative(head, refs))) { *nr -= refs; return 0; } @@ -151,7 +153,8 @@ static int gup_huge_pud(pud_t *pudp, pud_t pud, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - if (!page_cache_add_speculative(head, refs)) { + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_add_speculative(head, refs))) { *nr -= refs; return 0; } -- 2.24.0
On Fri, Nov 29, 2019 at 10:03:48AM +0100, Vlastimil Babka wrote:
>This collection of patches add the missing overflow checks in arch-specific
>gup.c variants for x86 and s390. Those were missed in backport of 8fde12ca79af
>("mm: prevent get_user_pages() from overflowing page refcount") as mainline
>had a single gup.c implementation at that point. See individual patches for
>details.
Queued up, thanks!
--
Thanks,
Sasha
On Fri, 2019-11-29 at 10:03 +0100, Vlastimil Babka wrote: > The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from > overflowing page refcount") was backported to 4.9.y stable as commit > 2ed768cfd895. The backport however missed that in 4.9, there are several > arch-specific gup.c versions with fast gup implementations, so these do not > prevent refcount overflow. > > This is partially fixed for x86 in stable-only commit d73af79742e7 ("x86, mm, > gup: prevent get_page() race with munmap in paravirt guest"). This stable-only > commit adds missing parts to x86 version, as well as s390 version, both taken > from the SUSE SLES/openSUSE 4.12-based kernels. > > The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely > the known overflow scenario based on FUSE, which needs 140GB of RAM, is a > problem for those architectures, and I don't feel confident enough to patch > them. > > Signed-off-by: Vlastimil Babka <vbabka@suse.cz> > --- > arch/s390/mm/gup.c | 9 ++++++--- > arch/x86/mm/gup.c | 10 ++++++++-- > 2 files changed, 14 insertions(+), 5 deletions(-) > > diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c > index 97fc449a7470..33a940389a6d 100644 > --- a/arch/s390/mm/gup.c > +++ b/arch/s390/mm/gup.c > @@ -38,7 +38,8 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr, > VM_BUG_ON(!pfn_valid(pte_pfn(pte))); > page = pte_page(pte); > head = compound_head(page); > - if (!page_cache_get_speculative(head)) > + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) No need for unlikely(); WARN_ON() includes that. > + || !page_cache_get_speculative(head))) > return 0; > if (unlikely(pte_val(pte) != pte_val(*ptep))) { > put_page(head); [...] > --- a/arch/x86/mm/gup.c > +++ b/arch/x86/mm/gup.c > @@ -202,10 +202,12 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr, > undo_dev_pagemap(nr, nr_start, pages); > return 0; > } > + if (unlikely(!try_get_page(page))) { > + put_dev_pagemap(pgmap); > + return 0; > + } > SetPageReferenced(page); > pages[*nr] = page; > - get_page(page); > - put_dev_pagemap(pgmap); This leaks a pgmap reference on success! > (*nr)++; > pfn++; > } while (addr += PAGE_SIZE, addr != end); > @@ -230,6 +232,8 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr, > > refs = 0; > head = pmd_page(pmd); > + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) Why <= 0, given we use < 0 elsewhere? > + return 0; > page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); > do { > VM_BUG_ON_PAGE(compound_head(page) != head, page); > @@ -289,6 +293,8 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr, > > refs = 0; > head = pud_page(pud); > + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) Same question here. Ben. > + return 0; > page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); > do { > VM_BUG_ON_PAGE(compound_head(page) != head, page); -- Ben Hutchings, Software Developer Codethink Ltd https://www.codethink.co.uk/ Dale House, 35 Dale Street Manchester, M1 2HF, United Kingdom
On 12/3/19 1:22 PM, Ben Hutchings wrote: >> + || !page_cache_get_speculative(head))) >> return 0; >> if (unlikely(pte_val(pte) != pte_val(*ptep))) { >> put_page(head); > [...] >> --- a/arch/x86/mm/gup.c >> +++ b/arch/x86/mm/gup.c >> @@ -202,10 +202,12 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr, >> undo_dev_pagemap(nr, nr_start, pages); >> return 0; >> } >> + if (unlikely(!try_get_page(page))) { >> + put_dev_pagemap(pgmap); >> + return 0; >> + } >> SetPageReferenced(page); >> pages[*nr] = page; >> - get_page(page); >> - put_dev_pagemap(pgmap); > > This leaks a pgmap reference on success! Good catch, deleted one line too many! >> (*nr)++; >> pfn++; >> } while (addr += PAGE_SIZE, addr != end); >> @@ -230,6 +232,8 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr, >> >> refs = 0; >> head = pmd_page(pmd); >> + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) > > Why <= 0, given we use < 0 elsewhere? The code uses get_head_page_multiple() which boils down to atomic_add and not add_unless_zero(), so it assumes a pre-existing pin that must not go away or it's a bug (one that I've been hunting recently in this area). The check makes it explicit. > >> + return 0; >> page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); >> do { >> VM_BUG_ON_PAGE(compound_head(page) != head, page); >> @@ -289,6 +293,8 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr, >> >> refs = 0; >> head = pud_page(pud); >> + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) > > Same question here. Same as above. > Ben. > >> + return 0; >> page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); >> do { >> VM_BUG_ON_PAGE(compound_head(page) != head, page);
On 12/1/19 5:55 PM, Sasha Levin wrote: > On Fri, Nov 29, 2019 at 10:03:48AM +0100, Vlastimil Babka wrote: >> This collection of patches add the missing overflow checks in arch-specific >> gup.c variants for x86 and s390. Those were missed in backport of 8fde12ca79af >> ("mm: prevent get_user_pages() from overflowing page refcount") as mainline >> had a single gup.c implementation at that point. See individual patches for >> details. > > Queued up, thanks! Please replace the 4.9 version with the following fixed one, thanks to Ben: ----8<---- From fe7f18bd152094f8516d79e847fcb5453a6f8368 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka <vbabka@suse.cz> Date: Wed, 6 Nov 2019 16:32:57 +0100 Subject: [PATCH] mm, gup: add missing refcount overflow checks on x86 and s390 The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from overflowing page refcount") was backported to 4.9.y stable as commit 2ed768cfd895. The backport however missed that in 4.9, there are several arch-specific gup.c versions with fast gup implementations, so these do not prevent refcount overflow. This is partially fixed for x86 in stable-only commit d73af79742e7 ("x86, mm, gup: prevent get_page() race with munmap in paravirt guest"). This stable-only commit adds missing parts to x86 version, as well as s390 version, both taken from the SUSE SLES/openSUSE 4.12-based kernels. The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely the known overflow scenario based on FUSE, which needs 140GB of RAM, is a problem for those architectures, and I don't feel confident enough to patch them. Signed-off-by: Vlastimil Babka <vbabka@suse.cz> --- arch/s390/mm/gup.c | 9 ++++++--- arch/x86/mm/gup.c | 9 ++++++++- 2 files changed, 14 insertions(+), 4 deletions(-) diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c index 97fc449a7470..cf045f56581e 100644 --- a/arch/s390/mm/gup.c +++ b/arch/s390/mm/gup.c @@ -38,7 +38,8 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr, VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte); head = compound_head(page); - if (!page_cache_get_speculative(head)) + if (WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_get_speculative(head)) return 0; if (unlikely(pte_val(pte) != pte_val(*ptep))) { put_page(head); @@ -76,7 +77,8 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - if (!page_cache_add_speculative(head, refs)) { + if (WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_add_speculative(head, refs)) { *nr -= refs; return 0; } @@ -150,7 +152,8 @@ static int gup_huge_pud(pud_t *pudp, pud_t pud, unsigned long addr, refs++; } while (addr += PAGE_SIZE, addr != end); - if (!page_cache_add_speculative(head, refs)) { + if (WARN_ON_ONCE(page_ref_count(head) < 0) + || !page_cache_add_speculative(head, refs)) { *nr -= refs; return 0; } diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index d7db45bdfb3b..82f727fbbbd2 100644 --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -202,9 +202,12 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr, undo_dev_pagemap(nr, nr_start, pages); return 0; } + if (unlikely(!try_get_page(page))) { + put_dev_pagemap(pgmap); + return 0; + } SetPageReferenced(page); pages[*nr] = page; - get_page(page); put_dev_pagemap(pgmap); (*nr)++; pfn++; @@ -230,6 +233,8 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr, refs = 0; head = pmd_page(pmd); + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) + return 0; page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); do { VM_BUG_ON_PAGE(compound_head(page) != head, page); @@ -289,6 +294,8 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr, refs = 0; head = pud_page(pud); + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) + return 0; page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); do { VM_BUG_ON_PAGE(compound_head(page) != head, page); -- 2.24.0
On Tue, Dec 03, 2019 at 01:50:26PM +0100, Vlastimil Babka wrote:
> On 12/1/19 5:55 PM, Sasha Levin wrote:
> > On Fri, Nov 29, 2019 at 10:03:48AM +0100, Vlastimil Babka wrote:
> >> This collection of patches add the missing overflow checks in arch-specific
> >> gup.c variants for x86 and s390. Those were missed in backport of 8fde12ca79af
> >> ("mm: prevent get_user_pages() from overflowing page refcount") as mainline
> >> had a single gup.c implementation at that point. See individual patches for
> >> details.
> >
> > Queued up, thanks!
>
> Please replace the 4.9 version with the following fixed one, thanks to Ben:
>
> ----8<----
> >From fe7f18bd152094f8516d79e847fcb5453a6f8368 Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Wed, 6 Nov 2019 16:32:57 +0100
> Subject: [PATCH] mm, gup: add missing refcount overflow checks on x86 and s390
>
> The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from
> overflowing page refcount") was backported to 4.9.y stable as commit
> 2ed768cfd895. The backport however missed that in 4.9, there are several
> arch-specific gup.c versions with fast gup implementations, so these do not
> prevent refcount overflow.
>
> This is partially fixed for x86 in stable-only commit d73af79742e7 ("x86, mm,
> gup: prevent get_page() race with munmap in paravirt guest"). This stable-only
> commit adds missing parts to x86 version, as well as s390 version, both taken
> from the SUSE SLES/openSUSE 4.12-based kernels.
>
> The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely
> the known overflow scenario based on FUSE, which needs 140GB of RAM, is a
> problem for those architectures, and I don't feel confident enough to patch
> them.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> arch/s390/mm/gup.c | 9 ++++++---
> arch/x86/mm/gup.c | 9 ++++++++-
> 2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
> index 97fc449a7470..cf045f56581e 100644
> --- a/arch/s390/mm/gup.c
> +++ b/arch/s390/mm/gup.c
> @@ -38,7 +38,8 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
> VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
> page = pte_page(pte);
> head = compound_head(page);
> - if (!page_cache_get_speculative(head))
> + if (WARN_ON_ONCE(page_ref_count(head) < 0)
> + || !page_cache_get_speculative(head))
> return 0;
> if (unlikely(pte_val(pte) != pte_val(*ptep))) {
> put_page(head);
> @@ -76,7 +77,8 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
> refs++;
> } while (addr += PAGE_SIZE, addr != end);
>
> - if (!page_cache_add_speculative(head, refs)) {
> + if (WARN_ON_ONCE(page_ref_count(head) < 0)
> + || !page_cache_add_speculative(head, refs)) {
> *nr -= refs;
> return 0;
> }
> @@ -150,7 +152,8 @@ static int gup_huge_pud(pud_t *pudp, pud_t pud, unsigned long addr,
> refs++;
> } while (addr += PAGE_SIZE, addr != end);
>
> - if (!page_cache_add_speculative(head, refs)) {
> + if (WARN_ON_ONCE(page_ref_count(head) < 0)
> + || !page_cache_add_speculative(head, refs)) {
> *nr -= refs;
> return 0;
> }
> diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
> index d7db45bdfb3b..82f727fbbbd2 100644
> --- a/arch/x86/mm/gup.c
> +++ b/arch/x86/mm/gup.c
> @@ -202,9 +202,12 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
> undo_dev_pagemap(nr, nr_start, pages);
> return 0;
> }
> + if (unlikely(!try_get_page(page))) {
> + put_dev_pagemap(pgmap);
> + return 0;
> + }
> SetPageReferenced(page);
> pages[*nr] = page;
> - get_page(page);
> put_dev_pagemap(pgmap);
> (*nr)++;
> pfn++;
> @@ -230,6 +233,8 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
>
> refs = 0;
> head = pmd_page(pmd);
> + if (WARN_ON_ONCE(page_ref_count(head) <= 0))
> + return 0;
> page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> do {
> VM_BUG_ON_PAGE(compound_head(page) != head, page);
> @@ -289,6 +294,8 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
>
> refs = 0;
> head = pud_page(pud);
> + if (WARN_ON_ONCE(page_ref_count(head) <= 0))
> + return 0;
> page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> do {
> VM_BUG_ON_PAGE(compound_head(page) != head, page);
> --
> 2.24.0
>
>
>
Now updated, sorry I missed this earlier.
greg k-h