* [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() @ 2016-06-17 2:30 Naoya Horiguchi 2016-06-17 2:30 ` [PATCH v1 2/2] mm: rmap: call page_check_address() with sync enabled to avoid racy check Naoya Horiguchi 2016-06-17 8:40 ` [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() Kirill A. Shutemov 0 siblings, 2 replies; 9+ messages in thread From: Naoya Horiguchi @ 2016-06-17 2:30 UTC (permalink / raw) To: linux-mm Cc: Kirill A. Shutemov, Andrew Morton, Hugh Dickins, Mel Gorman, Michal Hocko, Vlastimil Babka, linux-kernel, Naoya Horiguchi, Naoya Horiguchi I found a race condition triggering VM_BUG_ON() in freeze_page(), when running a testcase with 3 processes: - process 1: keep writing thp, - process 2: keep clearing soft-dirty bits from virtual address of process 1 - process 3: call migratepages for process 1, The kernel message is like this: kernel BUG at /src/linux-dev/mm/huge_memory.c:3096! invalid opcode: 0000 [#1] SMP Modules linked in: cfg80211 rfkill crc32c_intel ppdev serio_raw pcspkr virtio_balloon virtio_console parport_pc parport pvpanic acpi_cpufreq tpm_tis tpm i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi floppy virtio_pci virtio_ring virtio CPU: 0 PID: 28863 Comm: migratepages Not tainted 4.6.0-v4.6-160602-0827-+ #2 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 task: ffff880037320000 ti: ffff88007cdd0000 task.ti: ffff88007cdd0000 RIP: 0010:[<ffffffff811f8e06>] [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 RSP: 0018:ffff88007cdd3b70 EFLAGS: 00010202 RAX: 0000000000000001 RBX: ffff88007c7b88c0 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000700000200 RDI: ffffea0003188000 RBP: ffff88007cdd3bb8 R08: 0000000000000001 R09: 00003ffffffff000 R10: ffff880000000000 R11: ffffc000001fffff R12: ffffea0003188000 R13: ffffea0003188000 R14: 0000000000000000 R15: 0400000000000080 FS: 00007f8ec241d740(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f8ec1f3ed20 CR3: 000000003707b000 CR4: 00000000000006f0 Stack: ffffffff8139ef6d ffffea00031c6280 ffff88011ffec000 0000000000000000 0000700000400000 0000700000200000 ffff88007cdd3d08 ffff8800dbbe3008 0400000000000080 ffff88007cdd3c20 ffffffff811dd0b1 ffff88007cdd3d68 Call Trace: [<ffffffff8139ef6d>] ? list_del+0xd/0x30 [<ffffffff811dd0b1>] queue_pages_pte_range+0x4d1/0x590 [<ffffffff811ca1a4>] __walk_page_range+0x204/0x4e0 [<ffffffff811ca4f1>] walk_page_range+0x71/0xf0 [<ffffffff811db935>] queue_pages_range+0x75/0x90 [<ffffffff811dcbe0>] ? queue_pages_hugetlb+0x190/0x190 [<ffffffff811dca50>] ? new_node_page+0xc0/0xc0 [<ffffffff811ddac0>] ? change_prot_numa+0x40/0x40 [<ffffffff811dc001>] migrate_to_node+0x71/0xd0 [<ffffffff811ddd73>] do_migrate_pages+0x1c3/0x210 [<ffffffff811de0b1>] SyS_migrate_pages+0x261/0x290 [<ffffffff816f53f2>] entry_SYSCALL_64_fastpath+0x1a/0xa4 Code: e8 b0 87 fb ff 0f 0b 48 c7 c6 30 32 9f 81 e8 a2 87 fb ff 0f 0b 48 c7 c6 b8 46 9f 81 e8 94 87 fb ff 0f 0b 85 c0 0f 84 3e fd ff ff <0f> 0b 85 c0 0f 85 a6 00 00 00 48 8b 75 c0 4c 89 f7 41 be f0 ff RIP [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 RSP <ffff88007cdd3b70> I'm not sure of the full scenario of the reproduction, but my debug showed that split_huge_pmd_address(freeze=true) returned without running main code of pmd splitting because pmd_present(*pmd) was 0. If this happens, the subsequent try_to_unmap() fails and returns non-zero (because page_mapcount() still > 0), and finally VM_BUG_ON() fires. This patch fixes it by adding a separate split_huge_pmd_address()'s variant for freeze=true and checking pmd's state within ptl for that case. I think that this change seems to fit the comment in split_huge_pmd_address() that says "Caller holds the mmap_sem write mode, so a huge pmd cannot materialize from under us." We don't hold mmap_sem write if called from split_huge_page(), so maybe there were some different assumptions between callers (split_huge_page() and vma_adjust_trans_huge().) Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> --- include/linux/huge_mm.h | 8 ++++---- mm/huge_memory.c | 50 +++++++++++++++++++++++++++++++++++++------------ mm/rmap.c | 3 +-- 3 files changed, 43 insertions(+), 18 deletions(-) diff --git v4.6/include/linux/huge_mm.h v4.6_patched/include/linux/huge_mm.h index d7b9e53..6fa4348 100644 --- v4.6/include/linux/huge_mm.h +++ v4.6_patched/include/linux/huge_mm.h @@ -108,8 +108,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, } while (0) -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, - bool freeze, struct page *page); +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, + unsigned long address, struct page *page); extern int hugepage_madvise(struct vm_area_struct *vma, unsigned long *vm_flags, int advice); @@ -177,8 +177,8 @@ static inline void deferred_split_huge_page(struct page *page) {} #define split_huge_pmd(__vma, __pmd, __address) \ do { } while (0) -static inline void split_huge_pmd_address(struct vm_area_struct *vma, - unsigned long address, bool freeze, struct page *page) {} +static inline void split_huge_pmd_address_freeze(struct vm_area_struct *vma, + unsigned long address, struct page *page) {} static inline int hugepage_madvise(struct vm_area_struct *vma, unsigned long *vm_flags, int advice) diff --git v4.6/mm/huge_memory.c v4.6_patched/mm/huge_memory.c index b49ee12..c48f22c 100644 --- v4.6/mm/huge_memory.c +++ v4.6_patched/mm/huge_memory.c @@ -2989,6 +2989,16 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); ptl = pmd_lock(mm, pmd); + if (freeze) { + /* + * If caller asks to setup a migration entries, we need a page + * to check pmd against. Otherwise we can end up replacing + * wrong page. + */ + VM_BUG_ON(freeze && !pmd_page(*pmd)); + if (!pmd_present(*pmd)) + goto out; + } if (pmd_trans_huge(*pmd)) { struct page *page = pmd_page(*pmd); if (PageMlocked(page)) @@ -3001,8 +3011,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE); } -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, - bool freeze, struct page *page) +static void split_huge_pmd_address(struct vm_area_struct *vma, + unsigned long address, struct page *page) { pgd_t *pgd; pud_t *pud; @@ -3019,12 +3029,6 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, pmd = pmd_offset(pud, address); if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) return; - - /* - * If caller asks to setup a migration entries, we need a page to check - * pmd against. Otherwise we can end up replacing wrong page. - */ - VM_BUG_ON(freeze && !page); if (page && page != pmd_page(*pmd)) return; @@ -3032,7 +3036,29 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, * Caller holds the mmap_sem write mode, so a huge pmd cannot * materialize from under us. */ - __split_huge_pmd(vma, pmd, address, freeze); + __split_huge_pmd(vma, pmd, address, false); +} + +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, + unsigned long address, struct page *page) +{ + pgd_t *pgd; + pud_t *pud; + pmd_t *pmd; + + pgd = pgd_offset(vma->vm_mm, address); + if (!pgd_present(*pgd)) + return; + + pud = pud_offset(pgd, address); + if (!pud_present(*pud)) + return; + + pmd = pmd_offset(pud, address); + if (pmd_none(*pmd)) + return; + + __split_huge_pmd(vma, pmd, address, true); } void vma_adjust_trans_huge(struct vm_area_struct *vma, @@ -3048,7 +3074,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, if (start & ~HPAGE_PMD_MASK && (start & HPAGE_PMD_MASK) >= vma->vm_start && (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end) - split_huge_pmd_address(vma, start, false, NULL); + split_huge_pmd_address(vma, start, NULL); /* * If the new end address isn't hpage aligned and it could @@ -3058,7 +3084,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, if (end & ~HPAGE_PMD_MASK && (end & HPAGE_PMD_MASK) >= vma->vm_start && (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end) - split_huge_pmd_address(vma, end, false, NULL); + split_huge_pmd_address(vma, end, NULL); /* * If we're also updating the vma->vm_next->vm_start, if the new @@ -3072,7 +3098,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, if (nstart & ~HPAGE_PMD_MASK && (nstart & HPAGE_PMD_MASK) >= next->vm_start && (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end) - split_huge_pmd_address(next, nstart, false, NULL); + split_huge_pmd_address(next, nstart, NULL); } } diff --git v4.6/mm/rmap.c v4.6_patched/mm/rmap.c index 307b555..4282b56 100644 --- v4.6/mm/rmap.c +++ v4.6_patched/mm/rmap.c @@ -1418,8 +1418,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, goto out; if (flags & TTU_SPLIT_HUGE_PMD) { - split_huge_pmd_address(vma, address, - flags & TTU_MIGRATION, page); + split_huge_pmd_address_freeze(vma, address, page); /* check if we have anything to do after split */ if (page_mapcount(page) == 0) goto out; -- 2.7.0 ^ permalink raw reply related [flat|nested] 9+ messages in thread
* [PATCH v1 2/2] mm: rmap: call page_check_address() with sync enabled to avoid racy check 2016-06-17 2:30 [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() Naoya Horiguchi @ 2016-06-17 2:30 ` Naoya Horiguchi 2016-06-17 8:40 ` [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() Kirill A. Shutemov 1 sibling, 0 replies; 9+ messages in thread From: Naoya Horiguchi @ 2016-06-17 2:30 UTC (permalink / raw) To: linux-mm Cc: Kirill A. Shutemov, Andrew Morton, Hugh Dickins, Mel Gorman, Michal Hocko, Vlastimil Babka, linux-kernel, Naoya Horiguchi, Naoya Horiguchi The previous patch addresses the race between split_huge_pmd_address() and someone changing the pmd. The fix is only for splitting of normal thp (i.e. pmd-mapped thp,) and for splitting of pte-mapped thp there still is the similar race. For splitting pte-mapped thp, the pte's conversion is done by try_to_unmap_one(TTU_MIGRATION). This function checks page_check_address() to get the target pte, but it can return NULL under some race, leading to VM_BUG_ON() in freeze_page(). Fortunately, page_check_address() already has an argument to decide whether we do a quick/racy check or not, so let's flip it when called from freeze_page(). Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> --- mm/rmap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git v4.6/mm/rmap.c v4.6_patched/mm/rmap.c index 4282b56..c357fb36 100644 --- v4.6/mm/rmap.c +++ v4.6_patched/mm/rmap.c @@ -1424,7 +1424,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, goto out; } - pte = page_check_address(page, mm, address, &ptl, 0); + pte = page_check_address(page, mm, address, &ptl, + PageTransCompound(page)); if (!pte) goto out; -- 2.7.0 ^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() 2016-06-17 2:30 [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() Naoya Horiguchi 2016-06-17 2:30 ` [PATCH v1 2/2] mm: rmap: call page_check_address() with sync enabled to avoid racy check Naoya Horiguchi @ 2016-06-17 8:40 ` Kirill A. Shutemov 2016-06-20 8:55 ` Naoya Horiguchi 1 sibling, 1 reply; 9+ messages in thread From: Kirill A. Shutemov @ 2016-06-17 8:40 UTC (permalink / raw) To: Naoya Horiguchi Cc: linux-mm, Andrew Morton, Hugh Dickins, Mel Gorman, Michal Hocko, Vlastimil Babka, linux-kernel, Naoya Horiguchi On Fri, Jun 17, 2016 at 11:30:03AM +0900, Naoya Horiguchi wrote: > I found a race condition triggering VM_BUG_ON() in freeze_page(), when running > a testcase with 3 processes: > - process 1: keep writing thp, > - process 2: keep clearing soft-dirty bits from virtual address of process 1 > - process 3: call migratepages for process 1, > > The kernel message is like this: > > kernel BUG at /src/linux-dev/mm/huge_memory.c:3096! > invalid opcode: 0000 [#1] SMP > Modules linked in: cfg80211 rfkill crc32c_intel ppdev serio_raw pcspkr virtio_balloon virtio_console parport_pc parport pvpanic acpi_cpufreq tpm_tis tpm i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi floppy virtio_pci virtio_ring virtio > CPU: 0 PID: 28863 Comm: migratepages Not tainted 4.6.0-v4.6-160602-0827-+ #2 > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > task: ffff880037320000 ti: ffff88007cdd0000 task.ti: ffff88007cdd0000 > RIP: 0010:[<ffffffff811f8e06>] [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 > RSP: 0018:ffff88007cdd3b70 EFLAGS: 00010202 > RAX: 0000000000000001 RBX: ffff88007c7b88c0 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: 0000000700000200 RDI: ffffea0003188000 > RBP: ffff88007cdd3bb8 R08: 0000000000000001 R09: 00003ffffffff000 > R10: ffff880000000000 R11: ffffc000001fffff R12: ffffea0003188000 > R13: ffffea0003188000 R14: 0000000000000000 R15: 0400000000000080 > FS: 00007f8ec241d740(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f8ec1f3ed20 CR3: 000000003707b000 CR4: 00000000000006f0 > Stack: > ffffffff8139ef6d ffffea00031c6280 ffff88011ffec000 0000000000000000 > 0000700000400000 0000700000200000 ffff88007cdd3d08 ffff8800dbbe3008 > 0400000000000080 ffff88007cdd3c20 ffffffff811dd0b1 ffff88007cdd3d68 > Call Trace: > [<ffffffff8139ef6d>] ? list_del+0xd/0x30 > [<ffffffff811dd0b1>] queue_pages_pte_range+0x4d1/0x590 > [<ffffffff811ca1a4>] __walk_page_range+0x204/0x4e0 > [<ffffffff811ca4f1>] walk_page_range+0x71/0xf0 > [<ffffffff811db935>] queue_pages_range+0x75/0x90 > [<ffffffff811dcbe0>] ? queue_pages_hugetlb+0x190/0x190 > [<ffffffff811dca50>] ? new_node_page+0xc0/0xc0 > [<ffffffff811ddac0>] ? change_prot_numa+0x40/0x40 > [<ffffffff811dc001>] migrate_to_node+0x71/0xd0 > [<ffffffff811ddd73>] do_migrate_pages+0x1c3/0x210 > [<ffffffff811de0b1>] SyS_migrate_pages+0x261/0x290 > [<ffffffff816f53f2>] entry_SYSCALL_64_fastpath+0x1a/0xa4 > Code: e8 b0 87 fb ff 0f 0b 48 c7 c6 30 32 9f 81 e8 a2 87 fb ff 0f 0b 48 c7 c6 b8 46 9f 81 e8 94 87 fb ff 0f 0b 85 c0 0f 84 3e fd ff ff <0f> 0b 85 c0 0f 85 a6 00 00 00 48 8b 75 c0 4c 89 f7 41 be f0 ff > RIP [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 > RSP <ffff88007cdd3b70> > > I'm not sure of the full scenario of the reproduction, but my debug showed that > split_huge_pmd_address(freeze=true) returned without running main code of pmd > splitting because pmd_present(*pmd) was 0. If this happens, the subsequent > try_to_unmap() fails and returns non-zero (because page_mapcount() still > 0), > and finally VM_BUG_ON() fires. > > This patch fixes it by adding a separate split_huge_pmd_address()'s variant > for freeze=true and checking pmd's state within ptl for that case. Checking pmd under ptl is right thing to do, but I want to understand the scenario first. Do you have code to trigger this? > I think that this change seems to fit the comment in split_huge_pmd_address() > that says "Caller holds the mmap_sem write mode, so a huge pmd cannot > materialize from under us." We don't hold mmap_sem write if called from > split_huge_page(), so maybe there were some different assumptions between > callers (split_huge_page() and vma_adjust_trans_huge().) > > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > --- > include/linux/huge_mm.h | 8 ++++---- > mm/huge_memory.c | 50 +++++++++++++++++++++++++++++++++++++------------ > mm/rmap.c | 3 +-- > 3 files changed, 43 insertions(+), 18 deletions(-) > > diff --git v4.6/include/linux/huge_mm.h v4.6_patched/include/linux/huge_mm.h > index d7b9e53..6fa4348 100644 > --- v4.6/include/linux/huge_mm.h > +++ v4.6_patched/include/linux/huge_mm.h > @@ -108,8 +108,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > } while (0) > > > -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > - bool freeze, struct page *page); > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > + unsigned long address, struct page *page); > > extern int hugepage_madvise(struct vm_area_struct *vma, > unsigned long *vm_flags, int advice); > @@ -177,8 +177,8 @@ static inline void deferred_split_huge_page(struct page *page) {} > #define split_huge_pmd(__vma, __pmd, __address) \ > do { } while (0) > > -static inline void split_huge_pmd_address(struct vm_area_struct *vma, > - unsigned long address, bool freeze, struct page *page) {} > +static inline void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > + unsigned long address, struct page *page) {} > > static inline int hugepage_madvise(struct vm_area_struct *vma, > unsigned long *vm_flags, int advice) > diff --git v4.6/mm/huge_memory.c v4.6_patched/mm/huge_memory.c > index b49ee12..c48f22c 100644 > --- v4.6/mm/huge_memory.c > +++ v4.6_patched/mm/huge_memory.c > @@ -2989,6 +2989,16 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); > ptl = pmd_lock(mm, pmd); > + if (freeze) { > + /* > + * If caller asks to setup a migration entries, we need a page > + * to check pmd against. Otherwise we can end up replacing > + * wrong page. > + */ > + VM_BUG_ON(freeze && !pmd_page(*pmd)); > + if (!pmd_present(*pmd)) This looks strange. I guess you need to propagate page from caller to check pmd_page() against it. And I'm not sure about !pmd_present() check. Do you say that without the check pmd_trans_huge() below will be taken? I'm confused. > + goto out; > + } > if (pmd_trans_huge(*pmd)) { > struct page *page = pmd_page(*pmd); > if (PageMlocked(page)) > @@ -3001,8 +3011,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE); > } > > -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > - bool freeze, struct page *page) > +static void split_huge_pmd_address(struct vm_area_struct *vma, > + unsigned long address, struct page *page) > { > pgd_t *pgd; > pud_t *pud; > @@ -3019,12 +3029,6 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > pmd = pmd_offset(pud, address); > if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) > return; > - > - /* > - * If caller asks to setup a migration entries, we need a page to check > - * pmd against. Otherwise we can end up replacing wrong page. > - */ > - VM_BUG_ON(freeze && !page); > if (page && page != pmd_page(*pmd)) > return; This check was introduced only for try_to_unmap_one(). Could you check if moving it under ptl in __split_huge_pmd() would help? > @@ -3032,7 +3036,29 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > * Caller holds the mmap_sem write mode, so a huge pmd cannot > * materialize from under us. > */ > - __split_huge_pmd(vma, pmd, address, freeze); > + __split_huge_pmd(vma, pmd, address, false); > +} > + > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > + unsigned long address, struct page *page) > +{ > + pgd_t *pgd; > + pud_t *pud; > + pmd_t *pmd; > + > + pgd = pgd_offset(vma->vm_mm, address); > + if (!pgd_present(*pgd)) > + return; > + > + pud = pud_offset(pgd, address); > + if (!pud_present(*pud)) > + return; > + > + pmd = pmd_offset(pud, address); > + if (pmd_none(*pmd)) > + return; > + > + __split_huge_pmd(vma, pmd, address, true); > } > > void vma_adjust_trans_huge(struct vm_area_struct *vma, > @@ -3048,7 +3074,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, > if (start & ~HPAGE_PMD_MASK && > (start & HPAGE_PMD_MASK) >= vma->vm_start && > (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end) > - split_huge_pmd_address(vma, start, false, NULL); > + split_huge_pmd_address(vma, start, NULL); > > /* > * If the new end address isn't hpage aligned and it could > @@ -3058,7 +3084,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, > if (end & ~HPAGE_PMD_MASK && > (end & HPAGE_PMD_MASK) >= vma->vm_start && > (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end) > - split_huge_pmd_address(vma, end, false, NULL); > + split_huge_pmd_address(vma, end, NULL); > > /* > * If we're also updating the vma->vm_next->vm_start, if the new > @@ -3072,7 +3098,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, > if (nstart & ~HPAGE_PMD_MASK && > (nstart & HPAGE_PMD_MASK) >= next->vm_start && > (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end) > - split_huge_pmd_address(next, nstart, false, NULL); > + split_huge_pmd_address(next, nstart, NULL); > } > } > > diff --git v4.6/mm/rmap.c v4.6_patched/mm/rmap.c > index 307b555..4282b56 100644 > --- v4.6/mm/rmap.c > +++ v4.6_patched/mm/rmap.c > @@ -1418,8 +1418,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > goto out; > > if (flags & TTU_SPLIT_HUGE_PMD) { > - split_huge_pmd_address(vma, address, > - flags & TTU_MIGRATION, page); > + split_huge_pmd_address_freeze(vma, address, page); > /* check if we have anything to do after split */ > if (page_mapcount(page) == 0) > goto out; > -- > 2.7.0 > -- Kirill A. Shutemov ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() 2016-06-17 8:40 ` [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() Kirill A. Shutemov @ 2016-06-20 8:55 ` Naoya Horiguchi 2016-06-20 9:32 ` Kirill A. Shutemov 0 siblings, 1 reply; 9+ messages in thread From: Naoya Horiguchi @ 2016-06-20 8:55 UTC (permalink / raw) To: Kirill A. Shutemov Cc: linux-mm, Andrew Morton, Hugh Dickins, Mel Gorman, Michal Hocko, Vlastimil Babka, linux-kernel, Naoya Horiguchi On Fri, Jun 17, 2016 at 11:40:41AM +0300, Kirill A. Shutemov wrote: > On Fri, Jun 17, 2016 at 11:30:03AM +0900, Naoya Horiguchi wrote: > > I found a race condition triggering VM_BUG_ON() in freeze_page(), when running > > a testcase with 3 processes: > > - process 1: keep writing thp, > > - process 2: keep clearing soft-dirty bits from virtual address of process 1 > > - process 3: call migratepages for process 1, > > > > The kernel message is like this: > > > > kernel BUG at /src/linux-dev/mm/huge_memory.c:3096! > > invalid opcode: 0000 [#1] SMP > > Modules linked in: cfg80211 rfkill crc32c_intel ppdev serio_raw pcspkr virtio_balloon virtio_console parport_pc parport pvpanic acpi_cpufreq tpm_tis tpm i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi floppy virtio_pci virtio_ring virtio > > CPU: 0 PID: 28863 Comm: migratepages Not tainted 4.6.0-v4.6-160602-0827-+ #2 > > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > > task: ffff880037320000 ti: ffff88007cdd0000 task.ti: ffff88007cdd0000 > > RIP: 0010:[<ffffffff811f8e06>] [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 > > RSP: 0018:ffff88007cdd3b70 EFLAGS: 00010202 > > RAX: 0000000000000001 RBX: ffff88007c7b88c0 RCX: 0000000000000000 > > RDX: 0000000000000000 RSI: 0000000700000200 RDI: ffffea0003188000 > > RBP: ffff88007cdd3bb8 R08: 0000000000000001 R09: 00003ffffffff000 > > R10: ffff880000000000 R11: ffffc000001fffff R12: ffffea0003188000 > > R13: ffffea0003188000 R14: 0000000000000000 R15: 0400000000000080 > > FS: 00007f8ec241d740(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 00007f8ec1f3ed20 CR3: 000000003707b000 CR4: 00000000000006f0 > > Stack: > > ffffffff8139ef6d ffffea00031c6280 ffff88011ffec000 0000000000000000 > > 0000700000400000 0000700000200000 ffff88007cdd3d08 ffff8800dbbe3008 > > 0400000000000080 ffff88007cdd3c20 ffffffff811dd0b1 ffff88007cdd3d68 > > Call Trace: > > [<ffffffff8139ef6d>] ? list_del+0xd/0x30 > > [<ffffffff811dd0b1>] queue_pages_pte_range+0x4d1/0x590 > > [<ffffffff811ca1a4>] __walk_page_range+0x204/0x4e0 > > [<ffffffff811ca4f1>] walk_page_range+0x71/0xf0 > > [<ffffffff811db935>] queue_pages_range+0x75/0x90 > > [<ffffffff811dcbe0>] ? queue_pages_hugetlb+0x190/0x190 > > [<ffffffff811dca50>] ? new_node_page+0xc0/0xc0 > > [<ffffffff811ddac0>] ? change_prot_numa+0x40/0x40 > > [<ffffffff811dc001>] migrate_to_node+0x71/0xd0 > > [<ffffffff811ddd73>] do_migrate_pages+0x1c3/0x210 > > [<ffffffff811de0b1>] SyS_migrate_pages+0x261/0x290 > > [<ffffffff816f53f2>] entry_SYSCALL_64_fastpath+0x1a/0xa4 > > Code: e8 b0 87 fb ff 0f 0b 48 c7 c6 30 32 9f 81 e8 a2 87 fb ff 0f 0b 48 c7 c6 b8 46 9f 81 e8 94 87 fb ff 0f 0b 85 c0 0f 84 3e fd ff ff <0f> 0b 85 c0 0f 85 a6 00 00 00 48 8b 75 c0 4c 89 f7 41 be f0 ff > > RIP [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 > > RSP <ffff88007cdd3b70> > > > > I'm not sure of the full scenario of the reproduction, but my debug showed that > > split_huge_pmd_address(freeze=true) returned without running main code of pmd > > splitting because pmd_present(*pmd) was 0. If this happens, the subsequent > > try_to_unmap() fails and returns non-zero (because page_mapcount() still > 0), > > and finally VM_BUG_ON() fires. > > > > This patch fixes it by adding a separate split_huge_pmd_address()'s variant > > for freeze=true and checking pmd's state within ptl for that case. > > Checking pmd under ptl is right thing to do, but I want to understand the > scenario first. > > Do you have code to trigger this? Here's the testcode (maybe takes 5-10 min to trigger.) background_migratepages() { local pid=$1 while kill -0 $pid 2> /dev/null ; do migratepages $pid 0 1 migratepages $pid 1 0 done } background_clear_refs() { local pid=$1 while kill -0 $pid 2> /dev/null ; do echo 4 > /proc/$pid/clear_refs 2> /dev/null done } while true ; do $(dirname $BASH_SOURCE)/thp_alloc & PID=$! sleep 0.$RANDOM background_migratepages $PID > /dev/null & background_clear_refs $PID > /dev/null & sleep 0.$RANDOM kill -9 $PID done # thp_alloc.c #include <stdio.h> #include <sys/mman.h> #include <string.h> int main(int argc, char **argv) { size_t size = 2*1024*1024*10; char *p = mmap((void *)0x700000000000UL, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); madvise(p, size, MADV_HUGEPAGE); while (1) memset(p, 0, size); } > > I think that this change seems to fit the comment in split_huge_pmd_address() > > that says "Caller holds the mmap_sem write mode, so a huge pmd cannot > > materialize from under us." We don't hold mmap_sem write if called from > > split_huge_page(), so maybe there were some different assumptions between > > callers (split_huge_page() and vma_adjust_trans_huge().) > > > > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > > --- > > include/linux/huge_mm.h | 8 ++++---- > > mm/huge_memory.c | 50 +++++++++++++++++++++++++++++++++++++------------ > > mm/rmap.c | 3 +-- > > 3 files changed, 43 insertions(+), 18 deletions(-) > > > > diff --git v4.6/include/linux/huge_mm.h v4.6_patched/include/linux/huge_mm.h > > index d7b9e53..6fa4348 100644 > > --- v4.6/include/linux/huge_mm.h > > +++ v4.6_patched/include/linux/huge_mm.h > > @@ -108,8 +108,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > } while (0) > > > > > > -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > > - bool freeze, struct page *page); > > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > > + unsigned long address, struct page *page); > > > > extern int hugepage_madvise(struct vm_area_struct *vma, > > unsigned long *vm_flags, int advice); > > @@ -177,8 +177,8 @@ static inline void deferred_split_huge_page(struct page *page) {} > > #define split_huge_pmd(__vma, __pmd, __address) \ > > do { } while (0) > > > > -static inline void split_huge_pmd_address(struct vm_area_struct *vma, > > - unsigned long address, bool freeze, struct page *page) {} > > +static inline void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > > + unsigned long address, struct page *page) {} > > > > static inline int hugepage_madvise(struct vm_area_struct *vma, > > unsigned long *vm_flags, int advice) > > diff --git v4.6/mm/huge_memory.c v4.6_patched/mm/huge_memory.c > > index b49ee12..c48f22c 100644 > > --- v4.6/mm/huge_memory.c > > +++ v4.6_patched/mm/huge_memory.c > > @@ -2989,6 +2989,16 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > > > mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); > > ptl = pmd_lock(mm, pmd); > > + if (freeze) { > > + /* > > + * If caller asks to setup a migration entries, we need a page > > + * to check pmd against. Otherwise we can end up replacing > > + * wrong page. > > + */ > > + VM_BUG_ON(freeze && !pmd_page(*pmd)); > > + if (!pmd_present(*pmd)) > > This looks strange. I guess you need to propagate page from caller to > check pmd_page() against it. > > And I'm not sure about !pmd_present() check. Do you say that without the > check pmd_trans_huge() below will be taken? I'm confused. Thanks, checking page == pmd_page() seems enough here. > > + goto out; > > + } > > if (pmd_trans_huge(*pmd)) { > > struct page *page = pmd_page(*pmd); > > if (PageMlocked(page)) > > @@ -3001,8 +3011,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE); > > } > > > > -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > > - bool freeze, struct page *page) > > +static void split_huge_pmd_address(struct vm_area_struct *vma, > > + unsigned long address, struct page *page) > > { > > pgd_t *pgd; > > pud_t *pud; > > @@ -3019,12 +3029,6 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > > pmd = pmd_offset(pud, address); > > if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) > > return; > > - > > - /* > > - * If caller asks to setup a migration entries, we need a page to check > > - * pmd against. Otherwise we can end up replacing wrong page. > > - */ > > - VM_BUG_ON(freeze && !page); > > if (page && page != pmd_page(*pmd)) > > return; > > This check was introduced only for try_to_unmap_one(). Could you check if > moving it under ptl in __split_huge_pmd() would help? yes, this should work. Attached the updated patch. I'll continue digging more and hopefully update it if something helpful is found. Thanks, Naoya Horiguchi --- From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Date: Mon, 20 Jun 2016 17:38:26 +0900 Subject: [PATCH v2] mm: thp: move pmd check inside ptl for freeze_page() I found a race condition triggering VM_BUG_ON() in freeze_page(), when running a testcase with 3 processes: - process 1: keep writing thp, - process 2: keep clearing soft-dirty bits from virtual address of process 1 - process 3: call migratepages for process 1, The kernel message is like this: kernel BUG at /src/linux-dev/mm/huge_memory.c:3096! invalid opcode: 0000 [#1] SMP Modules linked in: cfg80211 rfkill crc32c_intel ppdev serio_raw pcspkr virtio_balloon virtio_console parport_pc parport pvpanic acpi_cpufreq tpm_tis tpm i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi floppy virtio_pci virtio_ring virtio CPU: 0 PID: 28863 Comm: migratepages Not tainted 4.6.0-v4.6-160602-0827-+ #2 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 task: ffff880037320000 ti: ffff88007cdd0000 task.ti: ffff88007cdd0000 RIP: 0010:[<ffffffff811f8e06>] [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 RSP: 0018:ffff88007cdd3b70 EFLAGS: 00010202 RAX: 0000000000000001 RBX: ffff88007c7b88c0 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000700000200 RDI: ffffea0003188000 RBP: ffff88007cdd3bb8 R08: 0000000000000001 R09: 00003ffffffff000 R10: ffff880000000000 R11: ffffc000001fffff R12: ffffea0003188000 R13: ffffea0003188000 R14: 0000000000000000 R15: 0400000000000080 FS: 00007f8ec241d740(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f8ec1f3ed20 CR3: 000000003707b000 CR4: 00000000000006f0 Stack: ffffffff8139ef6d ffffea00031c6280 ffff88011ffec000 0000000000000000 0000700000400000 0000700000200000 ffff88007cdd3d08 ffff8800dbbe3008 0400000000000080 ffff88007cdd3c20 ffffffff811dd0b1 ffff88007cdd3d68 Call Trace: [<ffffffff8139ef6d>] ? list_del+0xd/0x30 [<ffffffff811dd0b1>] queue_pages_pte_range+0x4d1/0x590 [<ffffffff811ca1a4>] __walk_page_range+0x204/0x4e0 [<ffffffff811ca4f1>] walk_page_range+0x71/0xf0 [<ffffffff811db935>] queue_pages_range+0x75/0x90 [<ffffffff811dcbe0>] ? queue_pages_hugetlb+0x190/0x190 [<ffffffff811dca50>] ? new_node_page+0xc0/0xc0 [<ffffffff811ddac0>] ? change_prot_numa+0x40/0x40 [<ffffffff811dc001>] migrate_to_node+0x71/0xd0 [<ffffffff811ddd73>] do_migrate_pages+0x1c3/0x210 [<ffffffff811de0b1>] SyS_migrate_pages+0x261/0x290 [<ffffffff816f53f2>] entry_SYSCALL_64_fastpath+0x1a/0xa4 Code: e8 b0 87 fb ff 0f 0b 48 c7 c6 30 32 9f 81 e8 a2 87 fb ff 0f 0b 48 c7 c6 b8 46 9f 81 e8 94 87 fb ff 0f 0b 85 c0 0f 84 3e fd ff ff <0f> 0b 85 c0 0f 85 a6 00 00 00 48 8b 75 c0 4c 89 f7 41 be f0 ff RIP [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 RSP <ffff88007cdd3b70> I'm not sure of the full scenario of the reproduction, but my debug showed that split_huge_pmd_address(freeze=true) returned without running main code of pmd splitting because pmd_present(*pmd) was 0. If this happens, the subsequent try_to_unmap() fails and returns non-zero (because page_mapcount() still > 0), and finally VM_BUG_ON() fires. This patch fixes it by adding a separate split_huge_pmd_address()'s variant for freeze=true and checking pmd's state within ptl for that case. I think that this change seems to fit the comment in split_huge_pmd_address() that says "Caller holds the mmap_sem write mode, so a huge pmd cannot materialize from under us." We don't hold mmap_sem write if called from split_huge_page(), so maybe there were some different assumptions between callers (split_huge_page() and vma_adjust_trans_huge().) Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> --- Diff from v1: - passed page to __split_huge_pmd() - dropped unnecessary !pmd_present check - removed pmd_none check in split_huge_pmd_address_freeze because it's effectively done in __split_huge_pmd() with ptl. --- include/linux/huge_mm.h | 12 ++++++------ mm/huge_memory.c | 52 ++++++++++++++++++++++++++++++++++--------------- mm/rmap.c | 3 +-- 3 files changed, 43 insertions(+), 24 deletions(-) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index d7b9e5346fba..3c6bab32a35c 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -96,7 +96,7 @@ static inline int split_huge_page(struct page *page) void deferred_split_huge_page(struct page *page); void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long address, bool freeze); + unsigned long address, struct page *page, bool freeze); #define split_huge_pmd(__vma, __pmd, __address) \ do { \ @@ -104,12 +104,12 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, if (pmd_trans_huge(*____pmd) \ || pmd_devmap(*____pmd)) \ __split_huge_pmd(__vma, __pmd, __address, \ - false); \ + NULL, false); \ } while (0) -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, - bool freeze, struct page *page); +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, + unsigned long address, struct page *page); extern int hugepage_madvise(struct vm_area_struct *vma, unsigned long *vm_flags, int advice); @@ -177,8 +177,8 @@ static inline void deferred_split_huge_page(struct page *page) {} #define split_huge_pmd(__vma, __pmd, __address) \ do { } while (0) -static inline void split_huge_pmd_address(struct vm_area_struct *vma, - unsigned long address, bool freeze, struct page *page) {} +static inline void split_huge_pmd_address_freeze(struct vm_area_struct *vma, + unsigned long address, struct page *page) {} static inline int hugepage_madvise(struct vm_area_struct *vma, unsigned long *vm_flags, int advice) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index b49ee126d4d1..5b43f735506a 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2981,7 +2981,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, } void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long address, bool freeze) + unsigned long address, struct page *page, bool freeze) { spinlock_t *ptl; struct mm_struct *mm = vma->vm_mm; @@ -2989,6 +2989,16 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); ptl = pmd_lock(mm, pmd); + if (freeze) { + /* + * If caller asks to setup a migration entries, we need a page + * to check pmd against. Otherwise we can end up replacing + * wrong page. + */ + VM_BUG_ON(!page); + if (page != pmd_page(*pmd)) + goto out; + } if (pmd_trans_huge(*pmd)) { struct page *page = pmd_page(*pmd); if (PageMlocked(page)) @@ -3001,8 +3011,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE); } -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, - bool freeze, struct page *page) +static void split_huge_pmd_address(struct vm_area_struct *vma, + unsigned long address, struct page *page) { pgd_t *pgd; pud_t *pud; @@ -3019,20 +3029,30 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, pmd = pmd_offset(pud, address); if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) return; - - /* - * If caller asks to setup a migration entries, we need a page to check - * pmd against. Otherwise we can end up replacing wrong page. - */ - VM_BUG_ON(freeze && !page); - if (page && page != pmd_page(*pmd)) - return; - /* * Caller holds the mmap_sem write mode, so a huge pmd cannot * materialize from under us. */ - __split_huge_pmd(vma, pmd, address, freeze); + __split_huge_pmd(vma, pmd, address, page, false); +} + +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, + unsigned long address, struct page *page) +{ + pgd_t *pgd; + pud_t *pud; + pmd_t *pmd; + + pgd = pgd_offset(vma->vm_mm, address); + if (!pgd_present(*pgd)) + return; + + pud = pud_offset(pgd, address); + if (!pud_present(*pud)) + return; + + pmd = pmd_offset(pud, address); + __split_huge_pmd(vma, pmd, address, page, true); } void vma_adjust_trans_huge(struct vm_area_struct *vma, @@ -3048,7 +3068,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, if (start & ~HPAGE_PMD_MASK && (start & HPAGE_PMD_MASK) >= vma->vm_start && (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end) - split_huge_pmd_address(vma, start, false, NULL); + split_huge_pmd_address(vma, start, NULL); /* * If the new end address isn't hpage aligned and it could @@ -3058,7 +3078,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, if (end & ~HPAGE_PMD_MASK && (end & HPAGE_PMD_MASK) >= vma->vm_start && (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end) - split_huge_pmd_address(vma, end, false, NULL); + split_huge_pmd_address(vma, end, NULL); /* * If we're also updating the vma->vm_next->vm_start, if the new @@ -3072,7 +3092,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, if (nstart & ~HPAGE_PMD_MASK && (nstart & HPAGE_PMD_MASK) >= next->vm_start && (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end) - split_huge_pmd_address(next, nstart, false, NULL); + split_huge_pmd_address(next, nstart, NULL); } } diff --git a/mm/rmap.c b/mm/rmap.c index 307b555024ef..4282b56b8e9f 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1418,8 +1418,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, goto out; if (flags & TTU_SPLIT_HUGE_PMD) { - split_huge_pmd_address(vma, address, - flags & TTU_MIGRATION, page); + split_huge_pmd_address_freeze(vma, address, page); /* check if we have anything to do after split */ if (page_mapcount(page) == 0) goto out; -- 2.5.5 ^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() 2016-06-20 8:55 ` Naoya Horiguchi @ 2016-06-20 9:32 ` Kirill A. Shutemov 2016-06-21 15:04 ` Kirill A. Shutemov 0 siblings, 1 reply; 9+ messages in thread From: Kirill A. Shutemov @ 2016-06-20 9:32 UTC (permalink / raw) To: Naoya Horiguchi Cc: linux-mm, Andrew Morton, Hugh Dickins, Mel Gorman, Michal Hocko, Vlastimil Babka, linux-kernel, Naoya Horiguchi On Mon, Jun 20, 2016 at 08:55:03AM +0000, Naoya Horiguchi wrote: > On Fri, Jun 17, 2016 at 11:40:41AM +0300, Kirill A. Shutemov wrote: > > On Fri, Jun 17, 2016 at 11:30:03AM +0900, Naoya Horiguchi wrote: > > > I found a race condition triggering VM_BUG_ON() in freeze_page(), when running > > > a testcase with 3 processes: > > > - process 1: keep writing thp, > > > - process 2: keep clearing soft-dirty bits from virtual address of process 1 > > > - process 3: call migratepages for process 1, > > > > > > The kernel message is like this: > > > > > > kernel BUG at /src/linux-dev/mm/huge_memory.c:3096! > > > invalid opcode: 0000 [#1] SMP > > > Modules linked in: cfg80211 rfkill crc32c_intel ppdev serio_raw pcspkr virtio_balloon virtio_console parport_pc parport pvpanic acpi_cpufreq tpm_tis tpm i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi floppy virtio_pci virtio_ring virtio > > > CPU: 0 PID: 28863 Comm: migratepages Not tainted 4.6.0-v4.6-160602-0827-+ #2 > > > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > > > task: ffff880037320000 ti: ffff88007cdd0000 task.ti: ffff88007cdd0000 > > > RIP: 0010:[<ffffffff811f8e06>] [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 > > > RSP: 0018:ffff88007cdd3b70 EFLAGS: 00010202 > > > RAX: 0000000000000001 RBX: ffff88007c7b88c0 RCX: 0000000000000000 > > > RDX: 0000000000000000 RSI: 0000000700000200 RDI: ffffea0003188000 > > > RBP: ffff88007cdd3bb8 R08: 0000000000000001 R09: 00003ffffffff000 > > > R10: ffff880000000000 R11: ffffc000001fffff R12: ffffea0003188000 > > > R13: ffffea0003188000 R14: 0000000000000000 R15: 0400000000000080 > > > FS: 00007f8ec241d740(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > CR2: 00007f8ec1f3ed20 CR3: 000000003707b000 CR4: 00000000000006f0 > > > Stack: > > > ffffffff8139ef6d ffffea00031c6280 ffff88011ffec000 0000000000000000 > > > 0000700000400000 0000700000200000 ffff88007cdd3d08 ffff8800dbbe3008 > > > 0400000000000080 ffff88007cdd3c20 ffffffff811dd0b1 ffff88007cdd3d68 > > > Call Trace: > > > [<ffffffff8139ef6d>] ? list_del+0xd/0x30 > > > [<ffffffff811dd0b1>] queue_pages_pte_range+0x4d1/0x590 > > > [<ffffffff811ca1a4>] __walk_page_range+0x204/0x4e0 > > > [<ffffffff811ca4f1>] walk_page_range+0x71/0xf0 > > > [<ffffffff811db935>] queue_pages_range+0x75/0x90 > > > [<ffffffff811dcbe0>] ? queue_pages_hugetlb+0x190/0x190 > > > [<ffffffff811dca50>] ? new_node_page+0xc0/0xc0 > > > [<ffffffff811ddac0>] ? change_prot_numa+0x40/0x40 > > > [<ffffffff811dc001>] migrate_to_node+0x71/0xd0 > > > [<ffffffff811ddd73>] do_migrate_pages+0x1c3/0x210 > > > [<ffffffff811de0b1>] SyS_migrate_pages+0x261/0x290 > > > [<ffffffff816f53f2>] entry_SYSCALL_64_fastpath+0x1a/0xa4 > > > Code: e8 b0 87 fb ff 0f 0b 48 c7 c6 30 32 9f 81 e8 a2 87 fb ff 0f 0b 48 c7 c6 b8 46 9f 81 e8 94 87 fb ff 0f 0b 85 c0 0f 84 3e fd ff ff <0f> 0b 85 c0 0f 85 a6 00 00 00 48 8b 75 c0 4c 89 f7 41 be f0 ff > > > RIP [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 > > > RSP <ffff88007cdd3b70> > > > > > > I'm not sure of the full scenario of the reproduction, but my debug showed that > > > split_huge_pmd_address(freeze=true) returned without running main code of pmd > > > splitting because pmd_present(*pmd) was 0. If this happens, the subsequent > > > try_to_unmap() fails and returns non-zero (because page_mapcount() still > 0), > > > and finally VM_BUG_ON() fires. > > > > > > This patch fixes it by adding a separate split_huge_pmd_address()'s variant > > > for freeze=true and checking pmd's state within ptl for that case. > > > > Checking pmd under ptl is right thing to do, but I want to understand the > > scenario first. > > > > Do you have code to trigger this? > > Here's the testcode (maybe takes 5-10 min to trigger.) > > background_migratepages() { > local pid=$1 > > while kill -0 $pid 2> /dev/null ; do > migratepages $pid 0 1 > migratepages $pid 1 0 > done > } > > background_clear_refs() { > local pid=$1 > > while kill -0 $pid 2> /dev/null ; do > echo 4 > /proc/$pid/clear_refs 2> /dev/null > done > } > > while true ; do > $(dirname $BASH_SOURCE)/thp_alloc & > PID=$! > sleep 0.$RANDOM > background_migratepages $PID > /dev/null & > background_clear_refs $PID > /dev/null & > sleep 0.$RANDOM > kill -9 $PID > done > > > # thp_alloc.c > > #include <stdio.h> > #include <sys/mman.h> > #include <string.h> > > int main(int argc, char **argv) { > size_t size = 2*1024*1024*10; > char *p = mmap((void *)0x700000000000UL, size, PROT_READ|PROT_WRITE, > MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); > madvise(p, size, MADV_HUGEPAGE); > while (1) > memset(p, 0, size); > } I failed to trigger it myself so far, but I can see where race is comming from. > > > I think that this change seems to fit the comment in split_huge_pmd_address() > > > that says "Caller holds the mmap_sem write mode, so a huge pmd cannot > > > materialize from under us." We don't hold mmap_sem write if called from > > > split_huge_page(), so maybe there were some different assumptions between > > > callers (split_huge_page() and vma_adjust_trans_huge().) > > > > > > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > > > --- > > > include/linux/huge_mm.h | 8 ++++---- > > > mm/huge_memory.c | 50 +++++++++++++++++++++++++++++++++++++------------ > > > mm/rmap.c | 3 +-- > > > 3 files changed, 43 insertions(+), 18 deletions(-) > > > > > > diff --git v4.6/include/linux/huge_mm.h v4.6_patched/include/linux/huge_mm.h > > > index d7b9e53..6fa4348 100644 > > > --- v4.6/include/linux/huge_mm.h > > > +++ v4.6_patched/include/linux/huge_mm.h > > > @@ -108,8 +108,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > > } while (0) > > > > > > > > > -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > > > - bool freeze, struct page *page); > > > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > > > + unsigned long address, struct page *page); > > > > > > extern int hugepage_madvise(struct vm_area_struct *vma, > > > unsigned long *vm_flags, int advice); > > > @@ -177,8 +177,8 @@ static inline void deferred_split_huge_page(struct page *page) {} > > > #define split_huge_pmd(__vma, __pmd, __address) \ > > > do { } while (0) > > > > > > -static inline void split_huge_pmd_address(struct vm_area_struct *vma, > > > - unsigned long address, bool freeze, struct page *page) {} > > > +static inline void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > > > + unsigned long address, struct page *page) {} > > > > > > static inline int hugepage_madvise(struct vm_area_struct *vma, > > > unsigned long *vm_flags, int advice) > > > diff --git v4.6/mm/huge_memory.c v4.6_patched/mm/huge_memory.c > > > index b49ee12..c48f22c 100644 > > > --- v4.6/mm/huge_memory.c > > > +++ v4.6_patched/mm/huge_memory.c > > > @@ -2989,6 +2989,16 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > > > > > mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); > > > ptl = pmd_lock(mm, pmd); > > > + if (freeze) { > > > + /* > > > + * If caller asks to setup a migration entries, we need a page > > > + * to check pmd against. Otherwise we can end up replacing > > > + * wrong page. > > > + */ > > > + VM_BUG_ON(freeze && !pmd_page(*pmd)); > > > + if (!pmd_present(*pmd)) > > > > This looks strange. I guess you need to propagate page from caller to > > check pmd_page() against it. > > > > And I'm not sure about !pmd_present() check. Do you say that without the > > check pmd_trans_huge() below will be taken? I'm confused. > > Thanks, checking page == pmd_page() seems enough here. > > > > + goto out; > > > + } > > > if (pmd_trans_huge(*pmd)) { > > > struct page *page = pmd_page(*pmd); > > > if (PageMlocked(page)) > > > @@ -3001,8 +3011,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > > mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE); > > > } > > > > > > -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > > > - bool freeze, struct page *page) > > > +static void split_huge_pmd_address(struct vm_area_struct *vma, > > > + unsigned long address, struct page *page) > > > { > > > pgd_t *pgd; > > > pud_t *pud; > > > @@ -3019,12 +3029,6 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > > > pmd = pmd_offset(pud, address); > > > if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) > > > return; > > > - > > > - /* > > > - * If caller asks to setup a migration entries, we need a page to check > > > - * pmd against. Otherwise we can end up replacing wrong page. > > > - */ > > > - VM_BUG_ON(freeze && !page); > > > if (page && page != pmd_page(*pmd)) > > > return; > > > > This check was introduced only for try_to_unmap_one(). Could you check if > > moving it under ptl in __split_huge_pmd() would help? > > yes, this should work. > > Attached the updated patch. I'll continue digging more and hopefully update it > if something helpful is found. > > Thanks, > Naoya Horiguchi > --- > From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > Date: Mon, 20 Jun 2016 17:38:26 +0900 > Subject: [PATCH v2] mm: thp: move pmd check inside ptl for freeze_page() > > I found a race condition triggering VM_BUG_ON() in freeze_page(), when running > a testcase with 3 processes: > - process 1: keep writing thp, > - process 2: keep clearing soft-dirty bits from virtual address of process 1 > - process 3: call migratepages for process 1, > > The kernel message is like this: > > kernel BUG at /src/linux-dev/mm/huge_memory.c:3096! > invalid opcode: 0000 [#1] SMP > Modules linked in: cfg80211 rfkill crc32c_intel ppdev serio_raw pcspkr virtio_balloon virtio_console parport_pc parport pvpanic acpi_cpufreq tpm_tis tpm i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi floppy virtio_pci virtio_ring virtio > CPU: 0 PID: 28863 Comm: migratepages Not tainted 4.6.0-v4.6-160602-0827-+ #2 > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > task: ffff880037320000 ti: ffff88007cdd0000 task.ti: ffff88007cdd0000 > RIP: 0010:[<ffffffff811f8e06>] [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 > RSP: 0018:ffff88007cdd3b70 EFLAGS: 00010202 > RAX: 0000000000000001 RBX: ffff88007c7b88c0 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: 0000000700000200 RDI: ffffea0003188000 > RBP: ffff88007cdd3bb8 R08: 0000000000000001 R09: 00003ffffffff000 > R10: ffff880000000000 R11: ffffc000001fffff R12: ffffea0003188000 > R13: ffffea0003188000 R14: 0000000000000000 R15: 0400000000000080 > FS: 00007f8ec241d740(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f8ec1f3ed20 CR3: 000000003707b000 CR4: 00000000000006f0 > Stack: > ffffffff8139ef6d ffffea00031c6280 ffff88011ffec000 0000000000000000 > 0000700000400000 0000700000200000 ffff88007cdd3d08 ffff8800dbbe3008 > 0400000000000080 ffff88007cdd3c20 ffffffff811dd0b1 ffff88007cdd3d68 > Call Trace: > [<ffffffff8139ef6d>] ? list_del+0xd/0x30 > [<ffffffff811dd0b1>] queue_pages_pte_range+0x4d1/0x590 > [<ffffffff811ca1a4>] __walk_page_range+0x204/0x4e0 > [<ffffffff811ca4f1>] walk_page_range+0x71/0xf0 > [<ffffffff811db935>] queue_pages_range+0x75/0x90 > [<ffffffff811dcbe0>] ? queue_pages_hugetlb+0x190/0x190 > [<ffffffff811dca50>] ? new_node_page+0xc0/0xc0 > [<ffffffff811ddac0>] ? change_prot_numa+0x40/0x40 > [<ffffffff811dc001>] migrate_to_node+0x71/0xd0 > [<ffffffff811ddd73>] do_migrate_pages+0x1c3/0x210 > [<ffffffff811de0b1>] SyS_migrate_pages+0x261/0x290 > [<ffffffff816f53f2>] entry_SYSCALL_64_fastpath+0x1a/0xa4 > Code: e8 b0 87 fb ff 0f 0b 48 c7 c6 30 32 9f 81 e8 a2 87 fb ff 0f 0b 48 c7 c6 b8 46 9f 81 e8 94 87 fb ff 0f 0b 85 c0 0f 84 3e fd ff ff <0f> 0b 85 c0 0f 85 a6 00 00 00 48 8b 75 c0 4c 89 f7 41 be f0 ff > RIP [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 > RSP <ffff88007cdd3b70> > > I'm not sure of the full scenario of the reproduction, but my debug showed that > split_huge_pmd_address(freeze=true) returned without running main code of pmd > splitting because pmd_present(*pmd) was 0. If this happens, the subsequent > try_to_unmap() fails and returns non-zero (because page_mapcount() still > 0), > and finally VM_BUG_ON() fires. > > This patch fixes it by adding a separate split_huge_pmd_address()'s variant > for freeze=true and checking pmd's state within ptl for that case. > > I think that this change seems to fit the comment in split_huge_pmd_address() > that says "Caller holds the mmap_sem write mode, so a huge pmd cannot > materialize from under us." We don't hold mmap_sem write if called from > split_huge_page(), so maybe there were some different assumptions between > callers (split_huge_page() and vma_adjust_trans_huge().) > > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > --- > Diff from v1: > - passed page to __split_huge_pmd() > - dropped unnecessary !pmd_present check > - removed pmd_none check in split_huge_pmd_address_freeze because it's > effectively done in __split_huge_pmd() with ptl. > --- > include/linux/huge_mm.h | 12 ++++++------ > mm/huge_memory.c | 52 ++++++++++++++++++++++++++++++++++--------------- > mm/rmap.c | 3 +-- > 3 files changed, 43 insertions(+), 24 deletions(-) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index d7b9e5346fba..3c6bab32a35c 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -96,7 +96,7 @@ static inline int split_huge_page(struct page *page) > void deferred_split_huge_page(struct page *page); > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > - unsigned long address, bool freeze); > + unsigned long address, struct page *page, bool freeze); > > #define split_huge_pmd(__vma, __pmd, __address) \ > do { \ > @@ -104,12 +104,12 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > if (pmd_trans_huge(*____pmd) \ > || pmd_devmap(*____pmd)) \ > __split_huge_pmd(__vma, __pmd, __address, \ > - false); \ > + NULL, false); \ > } while (0) > > > -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > - bool freeze, struct page *page); > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > + unsigned long address, struct page *page); > > extern int hugepage_madvise(struct vm_area_struct *vma, > unsigned long *vm_flags, int advice); > @@ -177,8 +177,8 @@ static inline void deferred_split_huge_page(struct page *page) {} > #define split_huge_pmd(__vma, __pmd, __address) \ > do { } while (0) > > -static inline void split_huge_pmd_address(struct vm_area_struct *vma, > - unsigned long address, bool freeze, struct page *page) {} > +static inline void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > + unsigned long address, struct page *page) {} > > static inline int hugepage_madvise(struct vm_area_struct *vma, > unsigned long *vm_flags, int advice) > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index b49ee126d4d1..5b43f735506a 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2981,7 +2981,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > } > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > - unsigned long address, bool freeze) > + unsigned long address, struct page *page, bool freeze) > { > spinlock_t *ptl; > struct mm_struct *mm = vma->vm_mm; > @@ -2989,6 +2989,16 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); > ptl = pmd_lock(mm, pmd); > + if (freeze) { > + /* > + * If caller asks to setup a migration entries, we need a page > + * to check pmd against. Otherwise we can end up replacing > + * wrong page. > + */ > + VM_BUG_ON(!page); > + if (page != pmd_page(*pmd)) > + goto out; > + } > if (pmd_trans_huge(*pmd)) { > struct page *page = pmd_page(*pmd); > if (PageMlocked(page)) > @@ -3001,8 +3011,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE); > } > > -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > - bool freeze, struct page *page) > +static void split_huge_pmd_address(struct vm_area_struct *vma, > + unsigned long address, struct page *page) > { > pgd_t *pgd; > pud_t *pud; > @@ -3019,20 +3029,30 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > pmd = pmd_offset(pud, address); > if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) > return; > - > - /* > - * If caller asks to setup a migration entries, we need a page to check > - * pmd against. Otherwise we can end up replacing wrong page. > - */ > - VM_BUG_ON(freeze && !page); > - if (page && page != pmd_page(*pmd)) > - return; > - > /* > * Caller holds the mmap_sem write mode, so a huge pmd cannot > * materialize from under us. > */ > - __split_huge_pmd(vma, pmd, address, freeze); > + __split_huge_pmd(vma, pmd, address, page, false); > +} > + > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > + unsigned long address, struct page *page) > +{ > + pgd_t *pgd; > + pud_t *pud; > + pmd_t *pmd; > + > + pgd = pgd_offset(vma->vm_mm, address); > + if (!pgd_present(*pgd)) > + return; > + > + pud = pud_offset(pgd, address); > + if (!pud_present(*pud)) > + return; > + > + pmd = pmd_offset(pud, address); > + __split_huge_pmd(vma, pmd, address, page, true); > } I don't see a reason to introduce new function. Just move the page check under ptl from split_huge_pmd_address() and that should be enough. Or am I missing something? > > void vma_adjust_trans_huge(struct vm_area_struct *vma, > @@ -3048,7 +3068,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, > if (start & ~HPAGE_PMD_MASK && > (start & HPAGE_PMD_MASK) >= vma->vm_start && > (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end) > - split_huge_pmd_address(vma, start, false, NULL); > + split_huge_pmd_address(vma, start, NULL); > > /* > * If the new end address isn't hpage aligned and it could > @@ -3058,7 +3078,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, > if (end & ~HPAGE_PMD_MASK && > (end & HPAGE_PMD_MASK) >= vma->vm_start && > (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end) > - split_huge_pmd_address(vma, end, false, NULL); > + split_huge_pmd_address(vma, end, NULL); > > /* > * If we're also updating the vma->vm_next->vm_start, if the new > @@ -3072,7 +3092,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, > if (nstart & ~HPAGE_PMD_MASK && > (nstart & HPAGE_PMD_MASK) >= next->vm_start && > (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end) > - split_huge_pmd_address(next, nstart, false, NULL); > + split_huge_pmd_address(next, nstart, NULL); > } > } > > diff --git a/mm/rmap.c b/mm/rmap.c > index 307b555024ef..4282b56b8e9f 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1418,8 +1418,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > goto out; > > if (flags & TTU_SPLIT_HUGE_PMD) { > - split_huge_pmd_address(vma, address, > - flags & TTU_MIGRATION, page); > + split_huge_pmd_address_freeze(vma, address, page); > /* check if we have anything to do after split */ > if (page_mapcount(page) == 0) > goto out; > -- > 2.5.5 > -- Kirill A. Shutemov ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() 2016-06-20 9:32 ` Kirill A. Shutemov @ 2016-06-21 15:04 ` Kirill A. Shutemov 2016-06-22 1:37 ` Naoya Horiguchi 0 siblings, 1 reply; 9+ messages in thread From: Kirill A. Shutemov @ 2016-06-21 15:04 UTC (permalink / raw) To: Naoya Horiguchi Cc: linux-mm, Andrew Morton, Hugh Dickins, Mel Gorman, Michal Hocko, Vlastimil Babka, linux-kernel, Naoya Horiguchi On Mon, Jun 20, 2016 at 12:32:01PM +0300, Kirill A. Shutemov wrote: > > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > > + unsigned long address, struct page *page) > > +{ > > + pgd_t *pgd; > > + pud_t *pud; > > + pmd_t *pmd; > > + > > + pgd = pgd_offset(vma->vm_mm, address); > > + if (!pgd_present(*pgd)) > > + return; > > + > > + pud = pud_offset(pgd, address); > > + if (!pud_present(*pud)) > > + return; > > + > > + pmd = pmd_offset(pud, address); > > + __split_huge_pmd(vma, pmd, address, page, true); > > } > > I don't see a reason to introduce new function. Just move the page > check under ptl from split_huge_pmd_address() and that should be enough. > > Or am I missing something? I'm talking about something like patch below. Could you test it? If it works fine to you, feel free to submit with my Signed-off-by. diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index eb810816bbc6..92ce91c03cd0 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -98,7 +98,7 @@ static inline int split_huge_page(struct page *page) void deferred_split_huge_page(struct page *page); void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long address, bool freeze); + unsigned long address, bool freeze, struct page *page); #define split_huge_pmd(__vma, __pmd, __address) \ do { \ @@ -106,7 +106,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, if (pmd_trans_huge(*____pmd) \ || pmd_devmap(*____pmd)) \ __split_huge_pmd(__vma, __pmd, __address, \ - false); \ + false, NULL); \ } while (0) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index eaf3a4a655a6..2297aa41581e 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1638,7 +1638,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, } void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long address, bool freeze) + unsigned long address, bool freeze, struct page *page) { spinlock_t *ptl; struct mm_struct *mm = vma->vm_mm; @@ -1646,8 +1646,17 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); ptl = pmd_lock(mm, pmd); + + /* + * If caller asks to setup a migration entries, we need a page to check + * pmd against. Otherwise we can end up replacing wrong page. + */ + VM_BUG_ON(freeze && !page); + if (page && page != pmd_page(*pmd)) + goto out; + if (pmd_trans_huge(*pmd)) { - struct page *page = pmd_page(*pmd); + page = pmd_page(*pmd); if (PageMlocked(page)) clear_page_mlock(page); } else if (!pmd_devmap(*pmd)) @@ -1678,20 +1687,12 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, return; /* - * If caller asks to setup a migration entries, we need a page to check - * pmd against. Otherwise we can end up replacing wrong page. - */ - VM_BUG_ON(freeze && !page); - if (page && page != pmd_page(*pmd)) - return; - - /* * Caller holds the mmap_sem write mode or the anon_vma lock, * so a huge pmd cannot materialize from under us (khugepaged * holds both the mmap_sem write mode and the anon_vma lock * write mode). */ - __split_huge_pmd(vma, pmd, address, freeze); + __split_huge_pmd(vma, pmd, address, freeze, page); } void vma_adjust_trans_huge(struct vm_area_struct *vma, -- Kirill A. Shutemov ^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() 2016-06-21 15:04 ` Kirill A. Shutemov @ 2016-06-22 1:37 ` Naoya Horiguchi 2016-06-22 2:42 ` Naoya Horiguchi 0 siblings, 1 reply; 9+ messages in thread From: Naoya Horiguchi @ 2016-06-22 1:37 UTC (permalink / raw) To: Kirill A. Shutemov Cc: linux-mm, Andrew Morton, Hugh Dickins, Mel Gorman, Michal Hocko, Vlastimil Babka, linux-kernel, Naoya Horiguchi On Tue, Jun 21, 2016 at 06:04:33PM +0300, Kirill A. Shutemov wrote: > On Mon, Jun 20, 2016 at 12:32:01PM +0300, Kirill A. Shutemov wrote: > > > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > > > + unsigned long address, struct page *page) > > > +{ > > > + pgd_t *pgd; > > > + pud_t *pud; > > > + pmd_t *pmd; > > > + > > > + pgd = pgd_offset(vma->vm_mm, address); > > > + if (!pgd_present(*pgd)) > > > + return; > > > + > > > + pud = pud_offset(pgd, address); > > > + if (!pud_present(*pud)) > > > + return; > > > + > > > + pmd = pmd_offset(pud, address); > > > + __split_huge_pmd(vma, pmd, address, page, true); > > > } > > > > I don't see a reason to introduce new function. Just move the page > > check under ptl from split_huge_pmd_address() and that should be enough. Sorry for my slow response (I was offline yesterday.) My point of separating function is to avoid checking pmd_present outside ptl just for freeze=true case (I didn't want affect other path, i.e. from vma_adjust_trans_huge().) But I think that the new function is unnecessary if we move the following part of split_huge_pmd_address() into ptl, if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) return; Does it make sense? > > Or am I missing something? > > I'm talking about something like patch below. Could you test it? Thanks, with this patch my 3-hour testing doesn't trigger the problem, so it works. But I feel it's weird because I think that the source of the race is "if (!pmd_present)" check in split_huge_pmd_address() called outside ptl. Your patch doesn't change that part, so I'm not sure why this fix works. > If it works fine to you, feel free to submit with my Signed-off-by. > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index eb810816bbc6..92ce91c03cd0 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -98,7 +98,7 @@ static inline int split_huge_page(struct page *page) > void deferred_split_huge_page(struct page *page); > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > - unsigned long address, bool freeze); > + unsigned long address, bool freeze, struct page *page); > > #define split_huge_pmd(__vma, __pmd, __address) \ > do { \ > @@ -106,7 +106,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > if (pmd_trans_huge(*____pmd) \ > || pmd_devmap(*____pmd)) \ > __split_huge_pmd(__vma, __pmd, __address, \ > - false); \ > + false, NULL); \ > } while (0) > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index eaf3a4a655a6..2297aa41581e 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1638,7 +1638,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > } > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > - unsigned long address, bool freeze) > + unsigned long address, bool freeze, struct page *page) > { > spinlock_t *ptl; > struct mm_struct *mm = vma->vm_mm; > @@ -1646,8 +1646,17 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); > ptl = pmd_lock(mm, pmd); > + > + /* > + * If caller asks to setup a migration entries, we need a page to check > + * pmd against. Otherwise we can end up replacing wrong page. > + */ > + VM_BUG_ON(freeze && !page); > + if (page && page != pmd_page(*pmd)) > + goto out; > + > if (pmd_trans_huge(*pmd)) { > - struct page *page = pmd_page(*pmd); > + page = pmd_page(*pmd); > if (PageMlocked(page)) > clear_page_mlock(page); > } else if (!pmd_devmap(*pmd)) > @@ -1678,20 +1687,12 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > return; > > /* > - * If caller asks to setup a migration entries, we need a page to check > - * pmd against. Otherwise we can end up replacing wrong page. > - */ > - VM_BUG_ON(freeze && !page); > - if (page && page != pmd_page(*pmd)) > - return; > - > - /* > * Caller holds the mmap_sem write mode or the anon_vma lock, > * so a huge pmd cannot materialize from under us (khugepaged > * holds both the mmap_sem write mode and the anon_vma lock > * write mode). Not a big issue, but this comment about mmap_sem seems relevant only when called from vma_adjust_trans_huge(), so might need some update? > */ > - __split_huge_pmd(vma, pmd, address, freeze); > + __split_huge_pmd(vma, pmd, address, freeze, page); > } > > void vma_adjust_trans_huge(struct vm_area_struct *vma, > -- > Kirill A. Shutemov > ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() 2016-06-22 1:37 ` Naoya Horiguchi @ 2016-06-22 2:42 ` Naoya Horiguchi 2016-06-22 11:16 ` Kirill A. Shutemov 0 siblings, 1 reply; 9+ messages in thread From: Naoya Horiguchi @ 2016-06-22 2:42 UTC (permalink / raw) To: Kirill A. Shutemov Cc: linux-mm, Andrew Morton, Hugh Dickins, Mel Gorman, Michal Hocko, Vlastimil Babka, linux-kernel, Naoya Horiguchi On Wed, Jun 22, 2016 at 01:37:00AM +0000, Horiguchi Naoya(堀口 直也) wrote: > On Tue, Jun 21, 2016 at 06:04:33PM +0300, Kirill A. Shutemov wrote: > > On Mon, Jun 20, 2016 at 12:32:01PM +0300, Kirill A. Shutemov wrote: > > > > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > > > > + unsigned long address, struct page *page) > > > > +{ > > > > + pgd_t *pgd; > > > > + pud_t *pud; > > > > + pmd_t *pmd; > > > > + > > > > + pgd = pgd_offset(vma->vm_mm, address); > > > > + if (!pgd_present(*pgd)) > > > > + return; > > > > + > > > > + pud = pud_offset(pgd, address); > > > > + if (!pud_present(*pud)) > > > > + return; > > > > + > > > > + pmd = pmd_offset(pud, address); > > > > + __split_huge_pmd(vma, pmd, address, page, true); > > > > } > > > > > > I don't see a reason to introduce new function. Just move the page > > > check under ptl from split_huge_pmd_address() and that should be enough. > > Sorry for my slow response (I was offline yesterday.) > > My point of separating function is to avoid checking pmd_present outside ptl > just for freeze=true case (I didn't want affect other path, > i.e. from vma_adjust_trans_huge().) > But I think that the new function is unnecessary if we move the following > part of split_huge_pmd_address() into ptl, > > if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) > return; > > Does it make sense? > > > > Or am I missing something? > > > > I'm talking about something like patch below. Could you test it? > > Thanks, with this patch my 3-hour testing doesn't trigger the problem, > so it works. But I feel it's weird because I think that the source of the > race is "if (!pmd_present)" check in split_huge_pmd_address() called outside ptl. > Your patch doesn't change that part, so I'm not sure why this fix works. Hmm, after sending previous email, I found the bug triggered with your patch. So I updated the patch with removing the prechecks. Thanks, Naoya Horiguchi --- From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Date: Wed, 22 Jun 2016 11:34:47 +0900 Subject: [PATCH] mm: thp: move pmd check inside ptl for freeze_page() I found a race condition triggering VM_BUG_ON() in freeze_page(), when running a testcase with 3 processes: - process 1: keep writing thp, - process 2: keep clearing soft-dirty bits from virtual address of process 1 - process 3: call migratepages for process 1, The kernel message is like this: kernel BUG at /src/linux-dev/mm/huge_memory.c:3096! invalid opcode: 0000 [#1] SMP Modules linked in: cfg80211 rfkill crc32c_intel ppdev serio_raw pcspkr virtio_balloon virtio_console parport_pc parport pvpanic acpi_cpufreq tpm_tis tpm i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi floppy virtio_pci virtio_ring virtio CPU: 0 PID: 28863 Comm: migratepages Not tainted 4.6.0-v4.6-160602-0827-+ #2 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 task: ffff880037320000 ti: ffff88007cdd0000 task.ti: ffff88007cdd0000 RIP: 0010:[<ffffffff811f8e06>] [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 RSP: 0018:ffff88007cdd3b70 EFLAGS: 00010202 RAX: 0000000000000001 RBX: ffff88007c7b88c0 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000700000200 RDI: ffffea0003188000 RBP: ffff88007cdd3bb8 R08: 0000000000000001 R09: 00003ffffffff000 R10: ffff880000000000 R11: ffffc000001fffff R12: ffffea0003188000 R13: ffffea0003188000 R14: 0000000000000000 R15: 0400000000000080 FS: 00007f8ec241d740(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f8ec1f3ed20 CR3: 000000003707b000 CR4: 00000000000006f0 Stack: ffffffff8139ef6d ffffea00031c6280 ffff88011ffec000 0000000000000000 0000700000400000 0000700000200000 ffff88007cdd3d08 ffff8800dbbe3008 0400000000000080 ffff88007cdd3c20 ffffffff811dd0b1 ffff88007cdd3d68 Call Trace: [<ffffffff8139ef6d>] ? list_del+0xd/0x30 [<ffffffff811dd0b1>] queue_pages_pte_range+0x4d1/0x590 [<ffffffff811ca1a4>] __walk_page_range+0x204/0x4e0 [<ffffffff811ca4f1>] walk_page_range+0x71/0xf0 [<ffffffff811db935>] queue_pages_range+0x75/0x90 [<ffffffff811dcbe0>] ? queue_pages_hugetlb+0x190/0x190 [<ffffffff811dca50>] ? new_node_page+0xc0/0xc0 [<ffffffff811ddac0>] ? change_prot_numa+0x40/0x40 [<ffffffff811dc001>] migrate_to_node+0x71/0xd0 [<ffffffff811ddd73>] do_migrate_pages+0x1c3/0x210 [<ffffffff811de0b1>] SyS_migrate_pages+0x261/0x290 [<ffffffff816f53f2>] entry_SYSCALL_64_fastpath+0x1a/0xa4 Code: e8 b0 87 fb ff 0f 0b 48 c7 c6 30 32 9f 81 e8 a2 87 fb ff 0f 0b 48 c7 c6 b8 46 9f 81 e8 94 87 fb ff 0f 0b 85 c0 0f 84 3e fd ff ff <0f> 0b 85 c0 0f 85 a6 00 00 00 48 8b 75 c0 4c 89 f7 41 be f0 ff RIP [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 RSP <ffff88007cdd3b70> I'm not sure of the full scenario of the reproduction, but my debug showed that split_huge_pmd_address(freeze=true) returned without running main code of pmd splitting because pmd_present(*pmd) in precheck somehow returned 0. If this happens, the subsequent try_to_unmap() fails and returns non-zero (because page_mapcount() still > 0), and finally VM_BUG_ON() fires. This patch tries to fix it by prechecking pmd state inside ptl. Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> --- Diff from v2: - don't use separate function Diff from v1: - passed page to __split_huge_pmd() - dropped unnecessary !pmd_present check - removed pmd_none check in split_huge_pmd_address_freeze because it's effectively done in __split_huge_pmd() with ptl. --- include/linux/huge_mm.h | 4 ++-- mm/huge_memory.c | 25 ++++++++++++------------- 2 files changed, 14 insertions(+), 15 deletions(-) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index d7b9e5346fba..a05ca41ae243 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -96,7 +96,7 @@ static inline int split_huge_page(struct page *page) void deferred_split_huge_page(struct page *page); void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long address, bool freeze); + unsigned long address, bool freeze, struct page *page); #define split_huge_pmd(__vma, __pmd, __address) \ do { \ @@ -104,7 +104,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, if (pmd_trans_huge(*____pmd) \ || pmd_devmap(*____pmd)) \ __split_huge_pmd(__vma, __pmd, __address, \ - false); \ + false, NULL); \ } while (0) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index b49ee126d4d1..44a3555c1d23 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2981,7 +2981,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, } void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long address, bool freeze) + unsigned long address, bool freeze, struct page *page) { spinlock_t *ptl; struct mm_struct *mm = vma->vm_mm; @@ -2989,8 +2989,17 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); ptl = pmd_lock(mm, pmd); + + /* + * If caller asks to setup a migration entries, we need a page to check + * pmd against. Otherwise we can end up replacing wrong page. + */ + VM_BUG_ON(freeze && !page); + if (page && page != pmd_page(*pmd)) + goto out; + if (pmd_trans_huge(*pmd)) { - struct page *page = pmd_page(*pmd); + page = pmd_page(*pmd); if (PageMlocked(page)) clear_page_mlock(page); } else if (!pmd_devmap(*pmd)) @@ -3017,22 +3026,12 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, return; pmd = pmd_offset(pud, address); - if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) - return; - - /* - * If caller asks to setup a migration entries, we need a page to check - * pmd against. Otherwise we can end up replacing wrong page. - */ - VM_BUG_ON(freeze && !page); - if (page && page != pmd_page(*pmd)) - return; /* * Caller holds the mmap_sem write mode, so a huge pmd cannot * materialize from under us. */ - __split_huge_pmd(vma, pmd, address, freeze); + __split_huge_pmd(vma, pmd, address, freeze, page); } void vma_adjust_trans_huge(struct vm_area_struct *vma, -- 2.5.5 ^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() 2016-06-22 2:42 ` Naoya Horiguchi @ 2016-06-22 11:16 ` Kirill A. Shutemov 0 siblings, 0 replies; 9+ messages in thread From: Kirill A. Shutemov @ 2016-06-22 11:16 UTC (permalink / raw) To: Naoya Horiguchi Cc: linux-mm, Andrew Morton, Hugh Dickins, Mel Gorman, Michal Hocko, Vlastimil Babka, linux-kernel, Naoya Horiguchi On Wed, Jun 22, 2016 at 02:42:25AM +0000, Naoya Horiguchi wrote: > On Wed, Jun 22, 2016 at 01:37:00AM +0000, Horiguchi Naoya(堀口 直也) wrote: > > On Tue, Jun 21, 2016 at 06:04:33PM +0300, Kirill A. Shutemov wrote: > > > On Mon, Jun 20, 2016 at 12:32:01PM +0300, Kirill A. Shutemov wrote: > > > > > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma, > > > > > + unsigned long address, struct page *page) > > > > > +{ > > > > > + pgd_t *pgd; > > > > > + pud_t *pud; > > > > > + pmd_t *pmd; > > > > > + > > > > > + pgd = pgd_offset(vma->vm_mm, address); > > > > > + if (!pgd_present(*pgd)) > > > > > + return; > > > > > + > > > > > + pud = pud_offset(pgd, address); > > > > > + if (!pud_present(*pud)) > > > > > + return; > > > > > + > > > > > + pmd = pmd_offset(pud, address); > > > > > + __split_huge_pmd(vma, pmd, address, page, true); > > > > > } > > > > > > > > I don't see a reason to introduce new function. Just move the page > > > > check under ptl from split_huge_pmd_address() and that should be enough. > > > > Sorry for my slow response (I was offline yesterday.) > > > > My point of separating function is to avoid checking pmd_present outside ptl > > just for freeze=true case (I didn't want affect other path, > > i.e. from vma_adjust_trans_huge().) > > But I think that the new function is unnecessary if we move the following > > part of split_huge_pmd_address() into ptl, > > > > if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) > > return; > > > > Does it make sense? > > > > > > Or am I missing something? > > > > > > I'm talking about something like patch below. Could you test it? > > > > Thanks, with this patch my 3-hour testing doesn't trigger the problem, > > so it works. But I feel it's weird because I think that the source of the > > race is "if (!pmd_present)" check in split_huge_pmd_address() called outside ptl. > > Your patch doesn't change that part, so I'm not sure why this fix works. > > Hmm, after sending previous email, I found the bug triggered with your patch. > So I updated the patch with removing the prechecks. > > Thanks, > Naoya Horiguchi > --- > From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > Date: Wed, 22 Jun 2016 11:34:47 +0900 > Subject: [PATCH] mm: thp: move pmd check inside ptl for freeze_page() > > I found a race condition triggering VM_BUG_ON() in freeze_page(), when running > a testcase with 3 processes: > - process 1: keep writing thp, > - process 2: keep clearing soft-dirty bits from virtual address of process 1 > - process 3: call migratepages for process 1, > > The kernel message is like this: > > kernel BUG at /src/linux-dev/mm/huge_memory.c:3096! > invalid opcode: 0000 [#1] SMP > Modules linked in: cfg80211 rfkill crc32c_intel ppdev serio_raw pcspkr virtio_balloon virtio_console parport_pc parport pvpanic acpi_cpufreq tpm_tis tpm i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi floppy virtio_pci virtio_ring virtio > CPU: 0 PID: 28863 Comm: migratepages Not tainted 4.6.0-v4.6-160602-0827-+ #2 > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > task: ffff880037320000 ti: ffff88007cdd0000 task.ti: ffff88007cdd0000 > RIP: 0010:[<ffffffff811f8e06>] [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 > RSP: 0018:ffff88007cdd3b70 EFLAGS: 00010202 > RAX: 0000000000000001 RBX: ffff88007c7b88c0 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: 0000000700000200 RDI: ffffea0003188000 > RBP: ffff88007cdd3bb8 R08: 0000000000000001 R09: 00003ffffffff000 > R10: ffff880000000000 R11: ffffc000001fffff R12: ffffea0003188000 > R13: ffffea0003188000 R14: 0000000000000000 R15: 0400000000000080 > FS: 00007f8ec241d740(0000) GS:ffff88007dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f8ec1f3ed20 CR3: 000000003707b000 CR4: 00000000000006f0 > Stack: > ffffffff8139ef6d ffffea00031c6280 ffff88011ffec000 0000000000000000 > 0000700000400000 0000700000200000 ffff88007cdd3d08 ffff8800dbbe3008 > 0400000000000080 ffff88007cdd3c20 ffffffff811dd0b1 ffff88007cdd3d68 > Call Trace: > [<ffffffff8139ef6d>] ? list_del+0xd/0x30 > [<ffffffff811dd0b1>] queue_pages_pte_range+0x4d1/0x590 > [<ffffffff811ca1a4>] __walk_page_range+0x204/0x4e0 > [<ffffffff811ca4f1>] walk_page_range+0x71/0xf0 > [<ffffffff811db935>] queue_pages_range+0x75/0x90 > [<ffffffff811dcbe0>] ? queue_pages_hugetlb+0x190/0x190 > [<ffffffff811dca50>] ? new_node_page+0xc0/0xc0 > [<ffffffff811ddac0>] ? change_prot_numa+0x40/0x40 > [<ffffffff811dc001>] migrate_to_node+0x71/0xd0 > [<ffffffff811ddd73>] do_migrate_pages+0x1c3/0x210 > [<ffffffff811de0b1>] SyS_migrate_pages+0x261/0x290 > [<ffffffff816f53f2>] entry_SYSCALL_64_fastpath+0x1a/0xa4 > Code: e8 b0 87 fb ff 0f 0b 48 c7 c6 30 32 9f 81 e8 a2 87 fb ff 0f 0b 48 c7 c6 b8 46 9f 81 e8 94 87 fb ff 0f 0b 85 c0 0f 84 3e fd ff ff <0f> 0b 85 c0 0f 85 a6 00 00 00 48 8b 75 c0 4c 89 f7 41 be f0 ff > RIP [<ffffffff811f8e06>] split_huge_page_to_list+0x496/0x590 > RSP <ffff88007cdd3b70> > > I'm not sure of the full scenario of the reproduction, but my debug showed that > split_huge_pmd_address(freeze=true) returned without running main code of pmd > splitting because pmd_present(*pmd) in precheck somehow returned 0. > If this happens, the subsequent try_to_unmap() fails and returns non-zero > (because page_mapcount() still > 0), and finally VM_BUG_ON() fires. > This patch tries to fix it by prechecking pmd state inside ptl. > > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > --- > Diff from v2: > - don't use separate function > > Diff from v1: > - passed page to __split_huge_pmd() > - dropped unnecessary !pmd_present check > - removed pmd_none check in split_huge_pmd_address_freeze because it's > effectively done in __split_huge_pmd() with ptl. > --- > include/linux/huge_mm.h | 4 ++-- > mm/huge_memory.c | 25 ++++++++++++------------- > 2 files changed, 14 insertions(+), 15 deletions(-) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index d7b9e5346fba..a05ca41ae243 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -96,7 +96,7 @@ static inline int split_huge_page(struct page *page) > void deferred_split_huge_page(struct page *page); > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > - unsigned long address, bool freeze); > + unsigned long address, bool freeze, struct page *page); > > #define split_huge_pmd(__vma, __pmd, __address) \ > do { \ > @@ -104,7 +104,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > if (pmd_trans_huge(*____pmd) \ > || pmd_devmap(*____pmd)) \ > __split_huge_pmd(__vma, __pmd, __address, \ > - false); \ > + false, NULL); \ > } while (0) > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index b49ee126d4d1..44a3555c1d23 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2981,7 +2981,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > } > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > - unsigned long address, bool freeze) > + unsigned long address, bool freeze, struct page *page) > { > spinlock_t *ptl; > struct mm_struct *mm = vma->vm_mm; > @@ -2989,8 +2989,17 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE); > ptl = pmd_lock(mm, pmd); > + > + /* > + * If caller asks to setup a migration entries, we need a page to check > + * pmd against. Otherwise we can end up replacing wrong page. > + */ > + VM_BUG_ON(freeze && !page); > + if (page && page != pmd_page(*pmd)) > + goto out; > + > if (pmd_trans_huge(*pmd)) { > - struct page *page = pmd_page(*pmd); > + page = pmd_page(*pmd); > if (PageMlocked(page)) > clear_page_mlock(page); > } else if (!pmd_devmap(*pmd)) > @@ -3017,22 +3026,12 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, > return; > > pmd = pmd_offset(pud, address); > - if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) > - return; > - > - /* > - * If caller asks to setup a migration entries, we need a page to check > - * pmd against. Otherwise we can end up replacing wrong page. > - */ > - VM_BUG_ON(freeze && !page); > - if (page && page != pmd_page(*pmd)) > - return; > > /* > * Caller holds the mmap_sem write mode, so a huge pmd cannot > * materialize from under us. > */ As you mentioned, the comment is no longer true. We should remove it (with separate patch?). Otherwise looks good to me. > - __split_huge_pmd(vma, pmd, address, freeze); > + __split_huge_pmd(vma, pmd, address, freeze, page); > } > > void vma_adjust_trans_huge(struct vm_area_struct *vma, > -- > 2.5.5 -- Kirill A. Shutemov ^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2016-06-22 12:09 UTC | newest] Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2016-06-17 2:30 [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() Naoya Horiguchi 2016-06-17 2:30 ` [PATCH v1 2/2] mm: rmap: call page_check_address() with sync enabled to avoid racy check Naoya Horiguchi 2016-06-17 8:40 ` [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page() Kirill A. Shutemov 2016-06-20 8:55 ` Naoya Horiguchi 2016-06-20 9:32 ` Kirill A. Shutemov 2016-06-21 15:04 ` Kirill A. Shutemov 2016-06-22 1:37 ` Naoya Horiguchi 2016-06-22 2:42 ` Naoya Horiguchi 2016-06-22 11:16 ` Kirill A. Shutemov
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