From 7f04c26d715a2467a49a2384268de8f70f787b51 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli Date: Sun, 30 Oct 2005 15:03:05 -0800 Subject: [PATCH] fix nr_unused accounting, and avoid recursing in iput with I_WILL_FREE set list_move(&inode->i_list, &inode_in_use); } else { list_move(&inode->i_list, &inode_unused); + inodes_stat.nr_unused++; } } wake_up_inode(inode); Are you sure the above diff is correct? It was added somewhere between 2.6.5 and 2.6.8. I think it's wrong. The only way I can imagine the i_count to be zero in the above path, is that I_WILL_FREE is set. And if I_WILL_FREE is set, then we must not increase nr_unused. So I believe the above change is buggy and it will definitely overstate the number of unused inodes and it should be backed out. Note that __writeback_single_inode before calling __sync_single_inode, can drop the spinlock and we can have both the dirty and locked bitflags clear here: spin_unlock(&inode_lock); __wait_on_inode(inode); iput(inode); XXXXXXX spin_lock(&inode_lock); } use inode again here a construct like the above makes zero sense from a reference counting standpoint. Either we don't ever use the inode again after the iput, or the inode_lock should be taken _before_ executing the iput (i.e. a __iput would be required). Taking the inode_lock after iput means the iget was useless if we keep using the inode after the iput. So the only chance the 2.6 was safe to call __writeback_single_inode with the i_count == 0, is that I_WILL_FREE is set (I_WILL_FREE will prevent the VM to free the inode in XXXXX). Potentially calling the above iput with I_WILL_FREE was also wrong because it would recurse in iput_final (the second mainline bug). The below (untested) patch fixes the nr_unused accounting, avoids recursing in iput when I_WILL_FREE is set and makes sure (with the BUG_ON) that we don't corrupt memory and that all holders that don't set I_WILL_FREE, keeps a reference on the inode! Signed-off-by: Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/fs-writeback.c | 28 ++++++++++++++++------------ 1 file changed, 16 insertions(+), 12 deletions(-) (limited to 'fs/fs-writeback.c') diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index e94ab398b717..ffab4783ac64 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -230,7 +230,6 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc) * The inode is clean, unused */ list_move(&inode->i_list, &inode_unused); - inodes_stat.nr_unused++; } } wake_up_inode(inode); @@ -238,14 +237,20 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc) } /* - * Write out an inode's dirty pages. Called under inode_lock. + * Write out an inode's dirty pages. Called under inode_lock. Either the + * caller has ref on the inode (either via __iget or via syscall against an fd) + * or the inode has I_WILL_FREE set (via generic_forget_inode) */ static int -__writeback_single_inode(struct inode *inode, - struct writeback_control *wbc) +__writeback_single_inode(struct inode *inode, struct writeback_control *wbc) { wait_queue_head_t *wqh; + if (!atomic_read(&inode->i_count)) + WARN_ON(!(inode->i_state & I_WILL_FREE)); + else + WARN_ON(inode->i_state & I_WILL_FREE); + if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_LOCK)) { list_move(&inode->i_list, &inode->i_sb->s_dirty); return 0; @@ -259,11 +264,9 @@ __writeback_single_inode(struct inode *inode, wqh = bit_waitqueue(&inode->i_state, __I_LOCK); do { - __iget(inode); spin_unlock(&inode_lock); __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE); - iput(inode); spin_lock(&inode_lock); } while (inode->i_state & I_LOCK); } @@ -541,14 +544,15 @@ void sync_inodes(int wait) } /** - * write_inode_now - write an inode to disk - * @inode: inode to write to disk - * @sync: whether the write should be synchronous or not + * write_inode_now - write an inode to disk + * @inode: inode to write to disk + * @sync: whether the write should be synchronous or not + * + * This function commits an inode to disk immediately if it is dirty. This is + * primarily needed by knfsd. * - * This function commits an inode to disk immediately if it is - * dirty. This is primarily needed by knfsd. + * The caller must either have a ref on the inode or must have set I_WILL_FREE. */ - int write_inode_now(struct inode *inode, int sync) { int ret; -- cgit v1.2.3