This fixes the following crash:
[ 63.976822] general protection fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 63.980094] CPU: 1 PID: 15 Comm: ksoftirqd/1 Not tainted 3.17.0-rc6+ #648
[ 63.980094] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 63.980094] task: ffff880117dea690 ti: ffff880117dfc000 task.ti: ffff880117dfc000
[ 63.980094] RIP: 0010:[<ffffffff817e6d07>] [<ffffffff817e6d07>] u32_destroy_key+0x27/0x6d
[ 63.980094] RSP: 0018:ffff880117dffcc0 EFLAGS: 00010202
[ 63.980094] RAX: ffff880117dea690 RBX: ffff8800d02e0820 RCX: 0000000000000000
[ 63.980094] RDX: 0000000000000001 RSI: 0000000000000002 RDI: 6b6b6b6b6b6b6b6b
[ 63.980094] RBP: ffff880117dffcd0 R08: 0000000000000000 R09: 0000000000000000
[ 63.980094] R10: 00006c0900006ba8 R11: 00006ba100006b9d R12: 0000000000000001
[ 63.980094] R13: ffff8800d02e0898 R14: ffffffff817e6d4d R15: ffff880117387a30
[ 63.980094] FS: 0000000000000000(0000) GS:ffff88011a800000(0000) knlGS:0000000000000000
[ 63.980094] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 63.980094] CR2: 00007f07e6732fed CR3: 000000011665b000 CR4: 00000000000006e0
[ 63.980094] Stack:
[ 63.980094] ffff88011a9cd300 ffffffff82051ac0 ffff880117dffce0 ffffffff817e6d68
[ 63.980094] ffff880117dffd70 ffffffff810cb4c7 ffffffff810cb3cd ffff880117dfffd8
[ 63.980094] ffff880117dea690 ffff880117dea690 ffff880117dfffd8 000000000000000a
[ 63.980094] Call Trace:
[ 63.980094] [<ffffffff817e6d68>] u32_delete_key_freepf_rcu+0x1b/0x1d
[ 63.980094] [<ffffffff810cb4c7>] rcu_process_callbacks+0x3bb/0x691
[ 63.980094] [<ffffffff810cb3cd>] ? rcu_process_callbacks+0x2c1/0x691
[ 63.980094] [<ffffffff817e6d4d>] ? u32_destroy_key+0x6d/0x6d
[ 63.980094] [<ffffffff810780a4>] __do_softirq+0x142/0x323
[ 63.980094] [<ffffffff810782a8>] run_ksoftirqd+0x23/0x53
[ 63.980094] [<ffffffff81092126>] smpboot_thread_fn+0x203/0x221
[ 63.980094] [<ffffffff81091f23>] ? smpboot_unpark_thread+0x33/0x33
[ 63.980094] [<ffffffff8108e44d>] kthread+0xc9/0xd1
[ 63.980094] [<ffffffff819e00ea>] ? do_wait_for_common+0xf8/0x125
[ 63.980094] [<ffffffff8108e384>] ? __kthread_parkme+0x61/0x61
[ 63.980094] [<ffffffff819e43ec>] ret_from_fork+0x7c/0xb0
[ 63.980094] [<ffffffff8108e384>] ? __kthread_parkme+0x61/0x61
tp could be freed in call_rcu callback too, the order is not guaranteed.
John Fastabend says:
====================
Its worth noting why this is safe. Any running schedulers will either
read the valid class field or it will be zeroed.
All schedulers today when the class is 0 do a lookup using the
same call used by the tcf_exts_bind(). So even if we have a running
classifier hit the null class pointer it will do a lookup and get
to the same result. This is particularly fragile at the moment because
the only way to verify this is to audit the schedulers call sites.
====================
Cc: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
a0efb80ce3