I think I found a race condition in some of the inode handling
code. Here's where I think it is:
1. Task A is inside kill_super(). It clears the MS_ACTIVE
flag of the s_flags field of the super_block struct and
calls invalidate_inodes(). In invalidate_inodes(), it
attempts to acquire inode_lock and spins because task B,
executing inside iput(), just decremented the reference
count of some inode i to 0 and acquired inode_lock.
2. Then the "if (!inode->i_nlink)" test condition evaluates
to false for task B so it executes the following chunk
of code:
01 } else {
02 if (!list_empty(&inode->i_hash)) {
03 if (!(inode->i_state & (I_DIRTY|I_LOCK))) {
04 list_del(&inode->i_list);
05 list_add(&inode->i_list, &inode_unused);
06 }
07 inodes_stat.nr_unused++;
08 spin_unlock(&inode_lock);
09 if (!sb || (sb->s_flags & MS_ACTIVE))
10 return;
11 write_inode_now(inode, 1);
12 spin_lock(&inode_lock);
13 inodes_stat.nr_unused--;
14 list_del_init(&inode->i_hash);
15 }
16 list_del_init(&inode->i_list);
17 inode->i_state|=I_FREEING;
18 inodes_stat.nr_inodes--;
19 spin_unlock(&inode_lock);
20 if (inode->i_data.nrpages)
21 truncate_inode_pages(&inode->i_data, 0);
22 clear_inode(inode);
23 }
24 destroy_inode(inode);
Now the test condition on line 02 evaluates to true, so
task B adds the inode to the inode_unused list and then
releases inode_lock on line 08.
3. Now A acquires inode_lock and B spins on inode_lock inside
write_inode_now();
4. Task A calls invalidate_list(), transferring inode i from
the inode_unused list to its own private throw_away list.
5. Task A releases inode_lock, allowing B to acquire inode_lock
and continue executing.
6. A attempts to destroy inode i inside dispose_list() while B
simultaneously attempts to destroy i, potentially causing
all sorts of bad things to happen.
So, did I find a bug or are my eyes playing tricks on me?
-Dave Peterson
dsp@llnl.gov
P.S. Please CC my email address when responding to this message.
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This archive was generated by hypermail 2b29 : Tue Apr 15 2003 - 22:00:36 EST