On Sat, Feb 28, 2015 at 02:45:38PM -0800, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
>
> The patch below does not apply to the 3.14-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
>
> thanks,
This patch depends on the following one:
commit 81d0fa623c5b8dbd5279d9713094b0f9b0a00fb4
Author: Peter Feiner <pfeiner@xxxxxxxxxx>
Date: Thu Oct 9 15:28:32 2014 -0700
mm: softdirty: unmapped addresses between VMAs are clean
Commit 81d0fa623c5b is cleanly applicable onto v3.14.34, so we can backport
05fbf357d941 with this patch.
As for the change in 81d0fa623c5b, I think the fix looks clear and simple
(contained in a single function,) so it's worth backporting as a stable fix too.
Or is there any reason that this 81d0fa623c5b was not tagged for stable trees?
Any idea, Peter?
Thanks,
Naoya Horiguchi
>
> greg k-h
>
> ------------------ original commit in Linus's tree ------------------
>
> From 05fbf357d94152171bc50f8a369390f1f16efd89 Mon Sep 17 00:00:00 2001
> From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> Date: Wed, 11 Feb 2015 15:27:31 -0800
> Subject: [PATCH] proc/pagemap: walk page tables under pte lock
>
> Lockless access to pte in pagemap_pte_range() might race with page
> migration and trigger BUG_ON(!PageLocked()) in migration_entry_to_page():
>
> CPU A (pagemap) CPU B (migration)
> lock_page()
> try_to_unmap(page, TTU_MIGRATION...)
> make_migration_entry()
> set_pte_at()
> <read *pte>
> pte_to_pagemap_entry()
> remove_migration_ptes()
> unlock_page()
> if(is_migration_entry())
> migration_entry_to_page()
> BUG_ON(!PageLocked(page))
>
> Also lockless read might be non-atomic if pte is larger than wordsize.
> Other pte walkers (smaps, numa_maps, clear_refs) already lock ptes.
>
> Fixes: 052fb0d635df ("proc: report file/anon bit in /proc/pid/pagemap")
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> Reported-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
> Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
> Acked-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> [3.5+]
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index e6e0abeb5d12..eeab30fcffcc 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1056,7 +1056,7 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> struct vm_area_struct *vma;
> struct pagemapread *pm = walk->private;
> spinlock_t *ptl;
> - pte_t *pte;
> + pte_t *pte, *orig_pte;
> int err = 0;
>
> /* find the first VMA at or above 'addr' */
> @@ -1117,15 +1117,19 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> BUG_ON(is_vm_hugetlb_page(vma));
>
> /* Addresses in the VMA. */
> - for (; addr < min(end, vma->vm_end); addr += PAGE_SIZE) {
> + orig_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> + for (; addr < min(end, vma->vm_end); pte++, addr += PAGE_SIZE) {
> pagemap_entry_t pme;
> - pte = pte_offset_map(pmd, addr);
> +
> pte_to_pagemap_entry(&pme, pm, vma, addr, *pte);
> - pte_unmap(pte);
> err = add_to_pagemap(addr, &pme, pm);
> if (err)
> - return err;
> + break;
> }
> + pte_unmap_unlock(orig_pte, ptl);
> +
> + if (err)
> + return err;
>
> if (addr == end)
> break;
> --
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