On 25-Sep-2014 04:33:20 PM, Matthew Wilcox wrote: > Pagecache faults recheck i_size after taking the page lock to ensure that > the fault didn't race against a truncate. We don't have a page to lock > in the XIP case, so use the i_mmap_mutex instead. It is locked in the > truncate path in unmap_mapping_range() after updating i_size. So while > we hold it in the fault path, we are guaranteed that either i_size has > already been updated in the truncate path, or that the truncate will > subsequently call zap_page_range_single() and so remove the mapping we > have just inserted. > > There is a window of time in which i_size has been reduced and the > thread has a mapping to a page which will be removed from the file, > but this is harmless as the page will not be allocated to a different > purpose before the thread's access to it is revoked. > > Signed-off-by: Matthew Wilcox <[email protected]> > Reviewed-by: Jan Kara <[email protected]> > Acked-by: Kirill A. Shutemov <[email protected]>
Reviewed-by: Mathieu Desnoyers <[email protected]> > --- > mm/filemap_xip.c | 24 ++++++++++++++++++++++-- > 1 file changed, 22 insertions(+), 2 deletions(-) > > diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c > index d8d9fe3..c8d23e9 100644 > --- a/mm/filemap_xip.c > +++ b/mm/filemap_xip.c > @@ -260,8 +260,17 @@ again: > __xip_unmap(mapping, vmf->pgoff); > > found: > + /* We must recheck i_size under i_mmap_mutex */ > + mutex_lock(&mapping->i_mmap_mutex); > + size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> > + PAGE_CACHE_SHIFT; > + if (unlikely(vmf->pgoff >= size)) { > + mutex_unlock(&mapping->i_mmap_mutex); > + return VM_FAULT_SIGBUS; > + } > err = vm_insert_mixed(vma, (unsigned long)vmf->virtual_address, > xip_pfn); > + mutex_unlock(&mapping->i_mmap_mutex); > if (err == -ENOMEM) > return VM_FAULT_OOM; > /* > @@ -285,16 +294,27 @@ found: > } > if (error != -ENODATA) > goto out; > + > + /* We must recheck i_size under i_mmap_mutex */ > + mutex_lock(&mapping->i_mmap_mutex); > + size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> > + PAGE_CACHE_SHIFT; > + if (unlikely(vmf->pgoff >= size)) { > + ret = VM_FAULT_SIGBUS; > + goto unlock; > + } > /* not shared and writable, use xip_sparse_page() */ > page = xip_sparse_page(); > if (!page) > - goto out; > + goto unlock; > err = vm_insert_page(vma, (unsigned long)vmf->virtual_address, > page); > if (err == -ENOMEM) > - goto out; > + goto unlock; > > ret = VM_FAULT_NOPAGE; > +unlock: > + mutex_unlock(&mapping->i_mmap_mutex); > out: > write_seqcount_end(&xip_sparse_seq); > mutex_unlock(&xip_sparse_mutex); > -- > 2.1.0 > > -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com Key fingerprint: 2A0B 4ED9 15F2 D3FA 45F5 B162 1728 0A97 8118 6ACF -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
