[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 <andrea@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index e94ab39..ffab478 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -230,7 +230,6 @@
* The inode is clean, unused
*/
list_move(&inode->i_list, &inode_unused);
- inodes_stat.nr_unused++;
}
}
wake_up_inode(inode);
@@ -238,14 +237,20 @@
}
/*
- * 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 @@
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 @@
}
/**
- * 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;