Re: [PATCH] fixed rtnl deadlock from gtp

On Tue, Oct 1, 2024 at 6:54 AM Daniel Yang [off-list ref] wrote:

Ok I see the issue. Yes it does seem to be a false positive. Then do we already have lockdep classes and subclasses set up for lock_sock() to prevent other false positives like this one? If not, should I add one then to resolve this?

Please  do not top post on linux mailing lists

About your question :
https://lore.kernel.org/netdev/CANn89iKcWmufo83xy-SwSrXYt6UpL2Pb+5pWuzyYjMva5F8bBQ@mail.gmail.com/ (local)

On Mon, Sep 30, 2024 at 8:04 PM Kuniyuki Iwashima [off-list ref] wrote:

quoted

From: Daniel Yang <redacted>
Date: Mon, 30 Sep 2024 18:55:54 -0700

quoted

Fixes deadlock described in this bug:
https://syzkaller.appspot.com/bug?extid=e953a8f3071f5c0a28fd.
Specific crash report here:
https://syzkaller.appspot.com/text?tag=CrashReport&x=14670e07980000.

DESCRIPTION OF ISSUE
Deadlock: sk_lock-AF_INET --> &smc->clcsock_release_lock --> rtnl_mutex

rtnl_mutex->sk_lock-AF_INET
rtnetlink_rcv_msg() acquires rtnl_lock() and calls rtnl_newlink(), which
eventually calls gtp_newlink() which calls lock_sock() to attempt to
acquire sk_lock.

Is the deadlock real ?

From the lockdep splat, the gtp's sk_protocol is verified to be
IPPROTO_UDP before holding lock_sock(), so it seems just a labeling
issue.
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/drivers/net/gtp.c?id=9410645520e9b820069761f3450ef6661418e279#n1674

quoted

sk_lock-AF_INET->&smc->clcsock_release_lock
smc_sendmsg() calls lock_sock() to acquire sk_lock, then calls
smc_switch_to_fallback() which attempts to acquire mutex_lock(&smc->...).

&smc->clcsock_release_lock->rtnl_mutex
smc_setsockopt() calls mutex_lock(&smc->...). smc->...->setsockopt() is
called, which calls nf_setsockopt() which attempts to acquire
rtnl_lock() in some nested call in start_sync_thread() in ip_vs_sync.c.

FIX:
In smc_switch_to_fallback(), separate the logic into inline function
__smc_switch_to_fallback(). In smc_sendmsg(), lock ordering can be
modified and the functionality of smc_switch_to_fallback() is
encapsulated in the __smc_switch_to_fallback() function.