From 4120db47198d21d8cd3b2cdbbe1ea6118a50bcd4 Mon Sep 17 00:00:00 2001 From: "Artem B. Bityuckiy" Date: Tue, 12 Jul 2005 13:58:12 -0700 Subject: [PATCH] [PATCH] bugfix: two read_inode() calls without clear_inode() call between Bug symptoms ~~~~~~~~~~~~ For the same inode VFS calls read_inode() twice and doesn't call clear_inode() between the two read_inode() invocations. Bug description ~~~~~~~~~~~~~~~ Suppose we have an inode which has zero reference count but is still in the inode cache. Suppose kswapd invokes shrink_icache_memory() to free some RAM. In prune_icache() inodes are removed from i_hash. prune_icache () is then going to call clear_inode(), but drops the inode_lock spinlock before this. If in this moment another task calls iget() for an inode which was just removed from i_hash by prune_icache(), then iget() invokes read_inode() for this inode, because it is *already removed* from i_hash. The end result is: we call iget(#N) then iput(#N); inode #N has zero i_count now and is in the inode cache; kswapd starts. kswapd removes the inode #N from i_hash ans is preempted; we call iget(#N) again; read_inode() is invoked as the result; but we expect clear_inode() before. Fix ~~~~~~~ To fix the bug I remove inodes from i_hash later, when clear_inode() is actually called. I remove them from i_hash under spinlock protection. Since the i_state is set to I_FREEING, it is safe to do this. The others will sleep waiting for the inode state change. I also postpone removing inodes from i_sb_list. It is not compulsory to do so but I do it for readability reasons. Inodes are added/removed to the lists together everywhere in the code and there is no point to change this rule. This is harmless because the only user of i_sb_list which somehow may interfere with me (invalidate_list()) is excluded by the iprune_sem mutex. The same race is possible in invalidate_list() so I do the same for it. Acked-by: Christoph Hellwig Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/inode.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/fs/inode.c b/fs/inode.c index 0116d06731c2..5bc97507eeaa 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -282,6 +282,13 @@ static void dispose_list(struct list_head *head) if (inode->i_data.nrpages) truncate_inode_pages(&inode->i_data, 0); clear_inode(inode); + + spin_lock(&inode_lock); + hlist_del_init(&inode->i_hash); + list_del_init(&inode->i_sb_list); + spin_unlock(&inode_lock); + + wake_up_inode(inode); destroy_inode(inode); nr_disposed++; } @@ -317,8 +324,6 @@ static int invalidate_list(struct list_head *head, struct list_head *dispose) inode = list_entry(tmp, struct inode, i_sb_list); invalidate_inode_buffers(inode); if (!atomic_read(&inode->i_count)) { - hlist_del_init(&inode->i_hash); - list_del(&inode->i_sb_list); list_move(&inode->i_list, dispose); inode->i_state |= I_FREEING; count++; @@ -439,8 +444,6 @@ static void prune_icache(int nr_to_scan) if (!can_unuse(inode)) continue; } - hlist_del_init(&inode->i_hash); - list_del_init(&inode->i_sb_list); list_move(&inode->i_list, &freeable); inode->i_state |= I_FREEING; nr_pruned++; -- 2.20.1