From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , alan@lxorguk.ukuu.org.uk, Hugh Dickins , Andrew Morton , Linus Torvalds Subject: [ 036/171] tmpfs: change final i_blocks BUG to WARNING Date: Wed, 21 Nov 2012 16:39:42 -0800 Message-Id: <20121122004036.994153524@linuxfoundation.org> In-Reply-To: <20121122004033.298367941@linuxfoundation.org> References: <20121122004033.298367941@linuxfoundation.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.4-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 Signed-off-by: Greg Kroah-Hartman --- mm/shmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/shmem.c +++ b/mm/shmem.c @@ -595,7 +595,7 @@ 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); end_writeback(inode); }