| Message ID | 1461015341-20153-18-git-send-email-jack@suse.cz (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Apr 18, 2016 at 11:35:40PM +0200, Jan Kara wrote: > When doing cow faults, we cannot directly fill in PTE as we do for other > faults as we rely on generic code to do proper accounting of the cowed page. > We also have no page to lock to protect against races with truncate as > other faults have and we need the protection to extend until the moment > generic code inserts cowed page into PTE thus at that point we have no > protection of fs-specific i_mmap_sem. So far we relied on using > i_mmap_lock for the protection however that is completely special to cow > faults. To make fault locking more uniform use DAX entry lock instead. > > Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com> > Signed-off-by: Jan Kara <jack@suse.cz> > --- > fs/dax.c | 12 +++++------- > include/linux/dax.h | 7 +++++++ > include/linux/mm.h | 7 +++++++ > mm/memory.c | 38 ++++++++++++++++++-------------------- > 4 files changed, 37 insertions(+), 27 deletions(-) > [...] > diff --git a/mm/memory.c b/mm/memory.c > index 93897f23cc11..f09cdb8d48fa 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -63,6 +63,7 @@ > #include <linux/dma-debug.h> > #include <linux/debugfs.h> > #include <linux/userfaultfd_k.h> > +#include <linux/dax.h> > > #include <asm/io.h> > #include <asm/mmu_context.h> > @@ -2785,7 +2786,8 @@ oom: > */ > static int __do_fault(struct vm_area_struct *vma, unsigned long address, > pgoff_t pgoff, unsigned int flags, > - struct page *cow_page, struct page **page) > + struct page *cow_page, struct page **page, > + void **entry) > { > struct vm_fault vmf; > int ret; > @@ -2800,8 +2802,10 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address, > ret = vma->vm_ops->fault(vma, &vmf); > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) > return ret; > - if (!vmf.page) > - goto out; Removing the above sounds seriously bogus to me as it means that below if (unlikely(PageHWPoison(vmf.page))) could dereference a NULL pointer. > + if (ret & VM_FAULT_DAX_LOCKED) { > + *entry = vmf.entry; > + return ret; > + } I see that below you call __do_fault() with NULL for entry, if i am properly understanding you will never get VM_FAULT_DAX_LOCKED set in those case so this should be fine but maybe a BUG_ON() might be worth it. > > if (unlikely(PageHWPoison(vmf.page))) { > if (ret & VM_FAULT_LOCKED) > @@ -2815,7 +2819,6 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address, > else > VM_BUG_ON_PAGE(!PageLocked(vmf.page), vmf.page); > > - out: > *page = vmf.page; > return ret; > } > @@ -2987,7 +2990,7 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma, > pte_unmap_unlock(pte, ptl); > } > > - ret = __do_fault(vma, address, pgoff, flags, NULL, &fault_page); > + ret = __do_fault(vma, address, pgoff, flags, NULL, &fault_page, NULL); > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) > return ret; > > @@ -3010,6 +3013,7 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma, > pgoff_t pgoff, unsigned int flags, pte_t orig_pte) > { > struct page *fault_page, *new_page; > + void *fault_entry; > struct mem_cgroup *memcg; > spinlock_t *ptl; > pte_t *pte; > @@ -3027,26 +3031,24 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma, > return VM_FAULT_OOM; > } > > - ret = __do_fault(vma, address, pgoff, flags, new_page, &fault_page); > + ret = __do_fault(vma, address, pgoff, flags, new_page, &fault_page, > + &fault_entry); > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) > goto uncharge_out; > > - if (fault_page) > + if (!(ret & VM_FAULT_DAX_LOCKED)) > copy_user_highpage(new_page, fault_page, address, vma); Again removing check for non NULL page looks bogus to me, i think there are still cases where you will get !(ret & VM_FAULT_DAX_LOCKED) and a fault_page == NULL, for instance from device file mapping. To me it seems that what you want is fault_page = NULL when VM_FAULT_DAX_LOCKED is set. > __SetPageUptodate(new_page); > > pte = pte_offset_map_lock(mm, pmd, address, &ptl); > if (unlikely(!pte_same(*pte, orig_pte))) { > pte_unmap_unlock(pte, ptl); > - if (fault_page) { > + if (!(ret & VM_FAULT_DAX_LOCKED)) { Same as above. > unlock_page(fault_page); > put_page(fault_page); > } else { > - /* > - * The fault handler has no page to lock, so it holds > - * i_mmap_lock for read to protect against truncate. > - */ > - i_mmap_unlock_read(vma->vm_file->f_mapping); > + dax_unlock_mapping_entry(vma->vm_file->f_mapping, > + pgoff); > } > goto uncharge_out; > } > @@ -3054,15 +3056,11 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma, > mem_cgroup_commit_charge(new_page, memcg, false, false); > lru_cache_add_active_or_unevictable(new_page, vma); > pte_unmap_unlock(pte, ptl); > - if (fault_page) { > + if (!(ret & VM_FAULT_DAX_LOCKED)) { Again fault_page might be NULL while VM_FAULT_DAX_LOCKED is not set. > unlock_page(fault_page); > put_page(fault_page); > } else { > - /* > - * The fault handler has no page to lock, so it holds > - * i_mmap_lock for read to protect against truncate. > - */ > - i_mmap_unlock_read(vma->vm_file->f_mapping); > + dax_unlock_mapping_entry(vma->vm_file->f_mapping, pgoff); > } > return ret; > uncharge_out: -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue 19-04-16 07:46:09, Jerome Glisse wrote: > On Mon, Apr 18, 2016 at 11:35:40PM +0200, Jan Kara wrote: > > diff --git a/mm/memory.c b/mm/memory.c > > index 93897f23cc11..f09cdb8d48fa 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -63,6 +63,7 @@ > > #include <linux/dma-debug.h> > > #include <linux/debugfs.h> > > #include <linux/userfaultfd_k.h> > > +#include <linux/dax.h> > > > > #include <asm/io.h> > > #include <asm/mmu_context.h> > > @@ -2785,7 +2786,8 @@ oom: > > */ > > static int __do_fault(struct vm_area_struct *vma, unsigned long address, > > pgoff_t pgoff, unsigned int flags, > > - struct page *cow_page, struct page **page) > > + struct page *cow_page, struct page **page, > > + void **entry) > > { > > struct vm_fault vmf; > > int ret; > > @@ -2800,8 +2802,10 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address, > > ret = vma->vm_ops->fault(vma, &vmf); > > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) > > return ret; > > - if (!vmf.page) > > - goto out; > > Removing the above sounds seriously bogus to me as it means that below > if (unlikely(PageHWPoison(vmf.page))) could dereference a NULL pointer. If you do not return a valid page, you must return appropriate return code from the ->fault handler. That being VM_FAULT_NOPAGE, VM_FAULT_DAX_LOCKED, or some error. That has always been the case except for DAX abuse which was added by commit 2e4cdab0584f "mm: allow page fault handlers to perform the COW" about an year ago. And my patch fixes this abuse. I'm not aware of any other code that would start abusing the return value from the ->fault handler. If some such code indeed got merged during the last year, it should be fixed as well. Honza
On Tue, Apr 19, 2016 at 04:33:43PM +0200, Jan Kara wrote: > On Tue 19-04-16 07:46:09, Jerome Glisse wrote: > > On Mon, Apr 18, 2016 at 11:35:40PM +0200, Jan Kara wrote: > > > diff --git a/mm/memory.c b/mm/memory.c > > > index 93897f23cc11..f09cdb8d48fa 100644 > > > --- a/mm/memory.c > > > +++ b/mm/memory.c > > > @@ -63,6 +63,7 @@ > > > #include <linux/dma-debug.h> > > > #include <linux/debugfs.h> > > > #include <linux/userfaultfd_k.h> > > > +#include <linux/dax.h> > > > > > > #include <asm/io.h> > > > #include <asm/mmu_context.h> > > > @@ -2785,7 +2786,8 @@ oom: > > > */ > > > static int __do_fault(struct vm_area_struct *vma, unsigned long address, > > > pgoff_t pgoff, unsigned int flags, > > > - struct page *cow_page, struct page **page) > > > + struct page *cow_page, struct page **page, > > > + void **entry) > > > { > > > struct vm_fault vmf; > > > int ret; > > > @@ -2800,8 +2802,10 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address, > > > ret = vma->vm_ops->fault(vma, &vmf); > > > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) > > > return ret; > > > - if (!vmf.page) > > > - goto out; > > > > Removing the above sounds seriously bogus to me as it means that below > > if (unlikely(PageHWPoison(vmf.page))) could dereference a NULL pointer. > > If you do not return a valid page, you must return appropriate return code > from the ->fault handler. That being VM_FAULT_NOPAGE, VM_FAULT_DAX_LOCKED, > or some error. That has always been the case except for DAX abuse which was > added by commit 2e4cdab0584f "mm: allow page fault handlers to perform the > COW" about an year ago. And my patch fixes this abuse. > > I'm not aware of any other code that would start abusing the return value > from the ->fault handler. If some such code indeed got merged during the > last year, it should be fixed as well. > Ok my bad i missed that. Cheers, Jérôme -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/dax.c b/fs/dax.c index be68d18a98c1..d907bf8b07a0 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -509,7 +509,7 @@ static void wake_mapping_entry_waiter(struct address_space *mapping, } } -static void unlock_mapping_entry(struct address_space *mapping, pgoff_t index) +void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index) { void *ret, **slot; @@ -532,7 +532,7 @@ static void put_locked_mapping_entry(struct address_space *mapping, unlock_page(entry); put_page(entry); } else { - unlock_mapping_entry(mapping, index); + dax_unlock_mapping_entry(mapping, index); } } @@ -912,12 +912,10 @@ int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf, goto unlock_entry; if (!radix_tree_exceptional_entry(entry)) { vmf->page = entry; - } else { - unlock_mapping_entry(mapping, vmf->pgoff); - i_mmap_lock_read(mapping); - vmf->page = NULL; + return VM_FAULT_LOCKED; } - return VM_FAULT_LOCKED; + vmf->entry = entry; + return VM_FAULT_DAX_LOCKED; } if (!buffer_mapped(&bh)) { diff --git a/include/linux/dax.h b/include/linux/dax.h index c5522f912344..ef94fa71368c 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -20,12 +20,19 @@ int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index); #ifdef CONFIG_FS_DAX struct page *read_dax_sector(struct block_device *bdev, sector_t n); +void dax_unlock_mapping_entry(struct address_space *mapping, pgoff_t index); #else static inline struct page *read_dax_sector(struct block_device *bdev, sector_t n) { return ERR_PTR(-ENXIO); } +/* Shouldn't ever be called when dax is disabled. */ +static inline void dax_unlock_mapping_entry(struct address_space *mapping, + pgoff_t index) +{ + BUG(); +} #endif #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_BROKEN) diff --git a/include/linux/mm.h b/include/linux/mm.h index a55e5be0894f..0ef9dc720ec3 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -299,6 +299,12 @@ struct vm_fault { * is set (which is also implied by * VM_FAULT_ERROR). */ + void *entry; /* ->fault handler can alternatively + * return locked DAX entry. In that + * case handler should return + * VM_FAULT_DAX_LOCKED and fill in + * entry here. + */ /* for ->map_pages() only */ pgoff_t max_pgoff; /* map pages for offset from pgoff till * max_pgoff inclusive */ @@ -1084,6 +1090,7 @@ static inline void clear_page_pfmemalloc(struct page *page) #define VM_FAULT_LOCKED 0x0200 /* ->fault locked the returned page */ #define VM_FAULT_RETRY 0x0400 /* ->fault blocked, must retry */ #define VM_FAULT_FALLBACK 0x0800 /* huge page fault failed, fall back to small */ +#define VM_FAULT_DAX_LOCKED 0x1000 /* ->fault has locked DAX entry */ #define VM_FAULT_HWPOISON_LARGE_MASK 0xf000 /* encodes hpage index for large hwpoison */ diff --git a/mm/memory.c b/mm/memory.c index 93897f23cc11..f09cdb8d48fa 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -63,6 +63,7 @@ #include <linux/dma-debug.h> #include <linux/debugfs.h> #include <linux/userfaultfd_k.h> +#include <linux/dax.h> #include <asm/io.h> #include <asm/mmu_context.h> @@ -2785,7 +2786,8 @@ oom: */ static int __do_fault(struct vm_area_struct *vma, unsigned long address, pgoff_t pgoff, unsigned int flags, - struct page *cow_page, struct page **page) + struct page *cow_page, struct page **page, + void **entry) { struct vm_fault vmf; int ret; @@ -2800,8 +2802,10 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address, ret = vma->vm_ops->fault(vma, &vmf); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) return ret; - if (!vmf.page) - goto out; + if (ret & VM_FAULT_DAX_LOCKED) { + *entry = vmf.entry; + return ret; + } if (unlikely(PageHWPoison(vmf.page))) { if (ret & VM_FAULT_LOCKED) @@ -2815,7 +2819,6 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address, else VM_BUG_ON_PAGE(!PageLocked(vmf.page), vmf.page); - out: *page = vmf.page; return ret; } @@ -2987,7 +2990,7 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma, pte_unmap_unlock(pte, ptl); } - ret = __do_fault(vma, address, pgoff, flags, NULL, &fault_page); + ret = __do_fault(vma, address, pgoff, flags, NULL, &fault_page, NULL); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) return ret; @@ -3010,6 +3013,7 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma, pgoff_t pgoff, unsigned int flags, pte_t orig_pte) { struct page *fault_page, *new_page; + void *fault_entry; struct mem_cgroup *memcg; spinlock_t *ptl; pte_t *pte; @@ -3027,26 +3031,24 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma, return VM_FAULT_OOM; } - ret = __do_fault(vma, address, pgoff, flags, new_page, &fault_page); + ret = __do_fault(vma, address, pgoff, flags, new_page, &fault_page, + &fault_entry); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) goto uncharge_out; - if (fault_page) + if (!(ret & VM_FAULT_DAX_LOCKED)) copy_user_highpage(new_page, fault_page, address, vma); __SetPageUptodate(new_page); pte = pte_offset_map_lock(mm, pmd, address, &ptl); if (unlikely(!pte_same(*pte, orig_pte))) { pte_unmap_unlock(pte, ptl); - if (fault_page) { + if (!(ret & VM_FAULT_DAX_LOCKED)) { unlock_page(fault_page); put_page(fault_page); } else { - /* - * The fault handler has no page to lock, so it holds - * i_mmap_lock for read to protect against truncate. - */ - i_mmap_unlock_read(vma->vm_file->f_mapping); + dax_unlock_mapping_entry(vma->vm_file->f_mapping, + pgoff); } goto uncharge_out; } @@ -3054,15 +3056,11 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma, mem_cgroup_commit_charge(new_page, memcg, false, false); lru_cache_add_active_or_unevictable(new_page, vma); pte_unmap_unlock(pte, ptl); - if (fault_page) { + if (!(ret & VM_FAULT_DAX_LOCKED)) { unlock_page(fault_page); put_page(fault_page); } else { - /* - * The fault handler has no page to lock, so it holds - * i_mmap_lock for read to protect against truncate. - */ - i_mmap_unlock_read(vma->vm_file->f_mapping); + dax_unlock_mapping_entry(vma->vm_file->f_mapping, pgoff); } return ret; uncharge_out: @@ -3082,7 +3080,7 @@ static int do_shared_fault(struct mm_struct *mm, struct vm_area_struct *vma, int dirtied = 0; int ret, tmp; - ret = __do_fault(vma, address, pgoff, flags, NULL, &fault_page); + ret = __do_fault(vma, address, pgoff, flags, NULL, &fault_page, NULL); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) return ret;