From patchwork Thu Dec 13 13:57:47 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [102/241] tmpfs: change final i_blocks BUG to WARNING Date: Thu, 13 Dec 2012 03:57:47 -0000 From: Herton Ronaldo Krzesinski X-Patchwork-Id: 205952 Message-Id: <1355407206-17100-103-git-send-email-herton.krzesinski@canonical.com> To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Linus Torvalds , Andrew Morton , Hugh Dickins 3.5.7.2 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Hugh Dickins 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [ herton: adjust context ] Signed-off-by: Herton Ronaldo Krzesinski --- mm/shmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/shmem.c b/mm/shmem.c index c7f7a77..8d0c102 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -654,7 +654,7 @@ static void shmem_evict_inode(struct inode *inode) kfree(xattr->name); kfree(xattr); } - BUG_ON(inode->i_blocks); + WARN_ON(inode->i_blocks); shmem_free_inode(inode->i_sb); clear_inode(inode); }