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dealing with the rest of shrink_dentry_list() livelock

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We have the same problem with ->d_lock order in the inner loop, where
we are dropping references to ancestors.  Same solution, basically -
instead of using dentry_kill() we use lock_parent() (introduced in the
previous commit) to get that lock in a safe way, recheck ->d_count
(in case if lock_parent() has ended up dropping and retaking ->d_lock
and somebody managed to grab a reference during that window), trylock
the inode->i_lock and use __dentry_kill() to do the rest.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2014-05-29 09:11:45 -04:00
parent 046b961b45
commit b2b80195d8
1 changed files with 20 additions and 2 deletions
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22
fs/dcache.c
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@ -885,8 +885,26 @@ static void shrink_dentry_list(struct list_head *list)
* fragmentation.
*/
dentry = parent;
while (dentry && !lockref_put_or_lock(&dentry->d_lockref))
dentry = dentry_kill(dentry, 1);
while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) {
parent = lock_parent(dentry);
if (dentry->d_lockref.count != 1) {
dentry->d_lockref.count--;
spin_unlock(&dentry->d_lock);
if (parent)
spin_unlock(&parent->d_lock);
break;
}
inode = dentry->d_inode; /* can't be NULL */
if (unlikely(!spin_trylock(&inode->i_lock))) {
spin_unlock(&dentry->d_lock);
if (parent)
spin_unlock(&parent->d_lock);
cpu_relax();
continue;
}
__dentry_kill(dentry);
dentry = parent;
}
}
}