| From | Greg Kroah-Hartman <> | Subject | [ 61/83] tmpfs: change final i_blocks BUG to WARNING | Date | Wed, 21 Nov 2012 16:42:23 -0800 |
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3.6-stable review patch. If anyone has any objections, please let me know.
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From: Hugh Dickins <hughd@google.com>
commit 0f3c42f522dc1ad7e27affc0a4aa8c790bce0a66 upstream.
Under a particular load on one machine, I have hit shmem_evict_inode()'s BUG_ON(inode->i_blocks), enough times to narrow it down to a particular race between swapout and eviction.
It comes from the "if (freed > 0)" asymmetry in shmem_recalc_inode(), and the lack of coherent locking between mapping's nrpages and shmem's swapped count. There's a window in shmem_writepage(), between lowering nrpages in shmem_delete_from_page_cache() and then raising swapped count, when the freed count appears to be +1 when it should be 0, and then the asymmetry stops it from being corrected with -1 before hitting the BUG.
One answer is coherent locking: using tree_lock throughout, without info->lock; reasonable, but the raw_spin_lock in percpu_counter_add() on used_blocks makes that messier than expected. Another answer may be a further effort to eliminate the weird shmem_recalc_inode() altogether, but previous attempts at that failed.
So far undecided, but for now change the BUG_ON to WARN_ON: in usual circumstances it remains a useful consistency check.
Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- mm/shmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/shmem.c +++ b/mm/shmem.c @@ -654,7 +654,7 @@ static void shmem_evict_inode(struct ino kfree(xattr->name); kfree(xattr); } - BUG_ON(inode->i_blocks); + WARN_ON(inode->i_blocks); shmem_free_inode(inode->i_sb); clear_inode(inode); }
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