Messages in this thread Patch in this message | | | Date | Tue, 18 Oct 2005 10:26:09 +0200 | From | Andrea Arcangeli <> | Subject | [PATCH] fix nr_unused accounting, and avoid recursing in iput with I_WILL_FREE set |
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Hello,
@@ -183,6 +183,7 @@ __sync_single_inode(struct inode *inode, 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!
Comments welcome, thanks.
Signed-off-by: Andrea Arcangeli <andrea@suse.de>
fs-writeback.c | 5 ++--- 1 files changed, 2 insertions(+), 3 deletions(-)
Index: linux-2.6/fs/fs-writeback.c --- linux-2.6/fs/fs-writeback.c.~1~ 2005-07-28 17:08:53.000000000 +0200 +++ linux-2.6/fs/fs-writeback.c 2005-10-17 15:43:53.000000000 +0200 @@ -230,7 +230,6 @@ __sync_single_inode(struct inode *inode, * The inode is clean, unused */ list_move(&inode->i_list, &inode_unused); - inodes_stat.nr_unused++; } } wake_up_inode(inode); @@ -246,6 +245,8 @@ __writeback_single_inode(struct inode *i { wait_queue_head_t *wqh; + BUG_ON(!atomic_read(&inode->i_count) ^ !!(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 +260,9 @@ __writeback_single_inode(struct inode *i 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); } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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