[PATCH v7 01/22] Fix XIP fault vs truncate race
From: Matthew Wilcox <hidden>
Date: 2014-03-23 19:08:27
Also in:
linux-fsdevel, lkml
Subsystem:
memory management, the rest · Maintainers:
Andrew Morton, Linus Torvalds
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 <redacted> --- 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);
--
1.9.0
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