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[PATCH] fix nr_unused accounting, and avoid recursing in iput with I_WILL_FREE set

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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>
This commit is contained in:
Andrea Arcangeli 2005-10-30 15:03:05 -08:00 committed by Linus Torvalds
parent 52303e8b5f
commit 7f04c26d71
2 changed files with 17 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

22
fs/fs-writeback.c
View file

@ -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);
}
@ -545,10 +548,11 @@ void sync_inodes(int wait)
* @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;

1
fs/inode.c
View file

@ -1088,6 +1088,7 @@ static void generic_forget_inode(struct inode *inode)
if (inode->i_data.nrpages)
truncate_inode_pages(&inode->i_data, 0);
clear_inode(inode);
wake_up_inode(inode);
destroy_inode(inode);
}