From: Johannes Berg <johannes@sipsolutions•net>
To: Hugh Dickins <hughd@google•com>
Cc: Linus Torvalds <torvalds@linux-foundation•org>,
Greg KH <gregkh@linuxfoundation•org>,
"David S. Miller" <davem@davemloft•net>,
"Otcheretianski, Andrei" <andrei.otcheretianski@intel•com>,
"linux-kernel@vger•kernel.org" <linux-kernel@vger•kernel.org>,
"netdev@vger•kernel.org" <netdev@vger•kernel.org>,
"stable@vger•kernel.org" <stable@vger•kernel.org>,
Pravin B Shelar <pshelar@nicira•com>, Thomas Graf <tgraf@suug•ch>
Subject: Re: 3.11-rc6 genetlink locking fix offends lockdep
Date: Mon, 19 Aug 2013 10:00:14 +0200 [thread overview]
Message-ID: <1376899214.14734.6.camel@jlt4.sipsolutions.net> (raw)
In-Reply-To: <alpine.LNX.2.00.1308182143370.906@eggly.anvils>
> 3.11-rc6's commit 58ad436fcf49 ("genetlink: fix family dump race")
> gives me the lockdep trace below at startup.
Hmm. Yes, I see now how this happens, not sure why I didn't run into it.
The problem is that genl_family_rcv_msg() is called with the genl_lock
held, and then calls netlink_dump_start() with it held, creating a
genl_lock->cb_mutex dependency, but obviously the dump continuation is
the other way around.
We could use the semaphore instead, I believe, but I don't really
understand the mutex vs. semaphore well enough to be sure that's
correct.
johannes
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index f85f8a2..6cfa646 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -792,7 +792,7 @@ static int ctrl_dumpfamily(struct sk_buff *skb, struct netlink_callback *cb)
bool need_locking = chains_to_skip || fams_to_skip;
if (need_locking)
- genl_lock();
+ down_read(&cb_lock);
for (i = chains_to_skip; i < GENL_FAM_TAB_SIZE; i++) {
n = 0;
@@ -815,7 +815,7 @@ errout:
cb->args[1] = n;
if (need_locking)
- genl_unlock();
+ up_read(&cb_lock);
return skb->len;
}
next prev parent reply other threads:[~2013-08-19 8:00 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-19 5:04 3.11-rc6 genetlink locking fix offends lockdep Hugh Dickins
2013-08-19 8:00 ` Johannes Berg [this message]
2013-08-19 11:00 ` Ding Tianhong
2013-08-19 11:22 ` Johannes Berg
2013-08-19 18:52 ` Hugh Dickins
2013-08-20 8:28 ` Johannes Berg
2013-08-20 9:04 ` Borislav Petkov
2013-08-20 15:49 ` Hugh Dickins
2013-08-20 19:02 ` Johannes Berg
2013-08-20 19:10 ` Johannes Berg
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