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Commit 16a100190d39592d1d56ff5a0b978b20288c3427

Authored by Hugh Dickins
Committed by Linus Torvalds
1 parent 1ae7000630
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

[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>

Showing 1 changed file with 8 additions and 0 deletions Side-by-side Diff

... ... @@ -674,8 +674,16 @@
674 674 * generic_delete_inode did it, before we lowered next_index.
675 675 * Also, though shmem_getpage checks i_size before adding to
676 676 * cache, no recheck after: so fix the narrow window there too.
  677 + *
  678 + * Recalling truncate_inode_pages_range and unmap_mapping_range
  679 + * every time for punch_hole (which never got a chance to clear
  680 + * SHMEM_PAGEIN at the start of vmtruncate_range) is expensive,
  681 + * yet hardly ever necessary: try to optimize them out later.
677 682 */
678 683 truncate_inode_pages_range(inode->i_mapping, start, end);
  684 + if (punch_hole)
  685 + unmap_mapping_range(inode->i_mapping, start,
  686 + end - start, 1);
679 687 }
680 688  
681 689 spin_lock(&info->lock);