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Date: Mon, 5 Nov 2012 17:34:56 -0800 (PST) From: Hugh Dickins <hughd@...gle.com> To: Andrew Morton <akpm@...ux-foundation.org> cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: [PATCH] tmpfs: change final i_blocks BUG to WARNING 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@...gle.com> Cc: stable@...r.kernel.org --- mm/shmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- 3.7-rc4/mm/shmem.c 2012-10-14 16:16:58.361309122 -0700 +++ linux/mm/shmem.c 2012-11-01 14:31:04.288185742 -0700 @@ -643,7 +643,7 @@ static void shmem_evict_inode(struct ino kfree(info->symlink); simple_xattrs_free(&info->xattrs); - BUG_ON(inode->i_blocks); + WARN_ON(inode->i_blocks); shmem_free_inode(inode->i_sb); clear_inode(inode); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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