dealing with the rest of shrink_dentry_list() livelock (b2b80195) · Commits · 戴 / test

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>

fs/dcache.c

+20 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}
		}
		}

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