Commit 16a10019 authored Mar 29, 2007 by Hugh Dickins Committed by Linus Torvalds Mar 29, 2007

[PATCH] holepunch: fix disconnected pages after second truncate



shmem_truncate_range has its own truncate_inode_pages_range, to free any pages
racily instantiated while it was in progress: a SHMEM_PAGEIN flag is set when
this might have happened.  But holepunching gets no chance to clear that flag
at the start of vmtruncate_range, so it's always set (unless a truncate came
just before), so holepunch almost always does this second
truncate_inode_pages_range.

shmem holepunch has unlikely swap<->file races hereabouts whatever we do
(without a fuller rework than is fit for this release): I was going to skip
the second truncate in the punch_hole case, but Miklos points out that would
make holepunch correctness more vulnerable to swapoff.  So keep the second
truncate, but follow it by an unmap_mapping_range to eliminate the
disconnected pages (freed from pagecache while still mapped in userspace) that
it might have left behind.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Miklos Szeredi <mszeredi@suse.cz>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 1ae70006

mm/shmem.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -674,8 +674,16 @@ done2:
		* generic_delete_inode did it, before we lowered next_index.
		* Also, though shmem_getpage checks i_size before adding to
		* cache, no recheck after: so fix the narrow window there too.
		*
		* Recalling truncate_inode_pages_range and unmap_mapping_range
		* every time for punch_hole (which never got a chance to clear
		* SHMEM_PAGEIN at the start of vmtruncate_range) is expensive,
		* yet hardly ever necessary: try to optimize them out later.
		*/
		truncate_inode_pages_range(inode->i_mapping, start, end);
		if (punch_hole)
		unmap_mapping_range(inode->i_mapping, start,
		end - start, 1);
		}

		spin_lock(&info->lock);