4b4b84468a
struct ip6_sf_socklist and ipv6_mc_socklist are per-socket MLD data.
These data are protected by rtnl lock, socket lock, and RCU.
So, when these are used, it verifies whether rtnl lock is acquired or not.
ip6_mc_msfget() is called by do_ipv6_getsockopt().
But caller doesn't acquire rtnl lock.
So, when these data are used in the ip6_mc_msfget() lockdep warns about it.
But accessing these is actually safe because socket lock was acquired by
do_ipv6_getsockopt().
So, it changes lockdep annotation from rtnl lock to socket lock.
(rtnl_dereference -> sock_dereference)
Locking graph for mld data is like below:
When writing mld data:
do_ipv6_setsockopt()
rtnl_lock
lock_sock
(mld functions)
idev->mc_lock(if per-interface mld data is modified)
When reading mld data:
do_ipv6_getsockopt()
lock_sock
ip6_mc_msfget()
Splat looks like:
=============================
WARNING: suspicious RCU usage
5.12.0-rc4+ #503 Not tainted
-----------------------------
net/ipv6/mcast.c:610 suspicious rcu_dereference_protected() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
1 lock held by mcast-listener-/923:
#0: ffff888007958a70 (sk_lock-AF_INET6){+.+.}-{0:0}, at:
ipv6_get_msfilter+0xaf/0x190
stack backtrace:
CPU: 1 PID: 923 Comm: mcast-listener- Not tainted 5.12.0-rc4+ #503
Call Trace:
dump_stack+0xa4/0xe5
ip6_mc_msfget+0x553/0x6c0
? ipv6_sock_mc_join_ssm+0x10/0x10
? lockdep_hardirqs_on_prepare+0x3e0/0x3e0
? mark_held_locks+0xb7/0x120
? lockdep_hardirqs_on_prepare+0x27c/0x3e0
? __local_bh_enable_ip+0xa5/0xf0
? lock_sock_nested+0x82/0xf0
ipv6_get_msfilter+0xc3/0x190
? compat_ipv6_get_msfilter+0x300/0x300
? lock_downgrade+0x690/0x690
do_ipv6_getsockopt.isra.6.constprop.13+0x1809/0x29e0
? do_ipv6_mcast_group_source+0x150/0x150
? register_lock_class+0x1750/0x1750
? kvm_sched_clock_read+0x14/0x30
? sched_clock+0x5/0x10
? sched_clock_cpu+0x18/0x170
? find_held_lock+0x3a/0x1c0
? lock_downgrade+0x690/0x690
? ipv6_getsockopt+0xdb/0x1b0
ipv6_getsockopt+0xdb/0x1b0
[ ... ]
Fixes: 88e2ca308094 ("mld: convert ifmcaddr6 to RCU")
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.