Commit 3ee6dafc authored Jul 19, 2007 by Miklos Szeredi Committed by Linus Torvalds Jul 19, 2007

only allow nonlinear vmas for ram backed filesystems



page_mkclean() doesn't re-protect ptes for non-linear mappings, so a later
re-dirty through such a mapping will not generate a fault, PG_dirty will
not reflect the dirty state and the dirty count will be skewed.  This
implies that msync() is also currently broken for nonlinear mappings.

The easiest solution is to emulate remap_file_pages on non-linear mappings
with simple mmap() for non ram-backed filesystems.  Applications continue
to work (albeit slower), as long as the number of remappings remain below
the maximum vma count.

However all currently known real uses of non-linear mappings are for ram
backed filesystems, which this patch doesn't affect.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: William Lee Irwin III <wli@holomorphy.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent bb2d5ce1

mm/fremap.c

+19 −0

Original line number	Diff line number	Diff line
		@@ -181,6 +181,25 @@ asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
		goto retry;
		}
		mapping = vma->vm_file->f_mapping;
		/*
		* page_mkclean doesn't work on nonlinear vmas, so if
		* dirty pages need to be accounted, emulate with linear
		* vmas.
		*/
		if (mapping_cap_account_dirty(mapping)) {
		unsigned long addr;

		flags &= MAP_NONBLOCK;
		addr = mmap_region(vma->vm_file, start, size,
		flags, vma->vm_flags, pgoff, 1);
		if (IS_ERR_VALUE(addr)) {
		err = addr;
		} else {
		BUG_ON(addr != start);
		err = 0;
		}
		goto out;
		}
		spin_lock(&mapping->i_mmap_lock);
		flush_dcache_mmap_lock(mapping);
		vma->vm_flags \|= VM_NONLINEAR;

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