From b11e3d782b9c065b3b2fb543bfb0d97801822dc0 Mon Sep 17 00:00:00 2001 From: "Srivatsa S. Bhat" Date: Wed, 7 Mar 2012 11:44:29 +0100 Subject: [PATCH] x86, mce: Fix rcu splat in drain_mce_log_buffer() While booting, the following message is seen: [ 21.665087] =============================== [ 21.669439] [ INFO: suspicious RCU usage. ] [ 21.673798] 3.2.0-0.0.0.28.36b5ec9-default #2 Not tainted [ 21.681353] ------------------------------- [ 21.685864] arch/x86/kernel/cpu/mcheck/mce.c:194 suspicious rcu_dereference_index_check() usage! [ 21.695013] [ 21.695014] other info that might help us debug this: [ 21.695016] [ 21.703488] [ 21.703489] rcu_scheduler_active = 1, debug_locks = 1 [ 21.710426] 3 locks held by modprobe/2139: [ 21.714754] #0: (&__lockdep_no_validate__){......}, at: [] __driver_attach+0x53/0xa0 [ 21.725020] #1: [ 21.725323] ioatdma: Intel(R) QuickData Technology Driver 4.00 [ 21.733206] (&__lockdep_no_validate__){......}, at: [] __driver_attach+0x61/0xa0 [ 21.743015] #2: (i7core_edac_lock){+.+.+.}, at: [] i7core_probe+0x1f/0x5c0 [i7core_edac] [ 21.753708] [ 21.753709] stack backtrace: [ 21.758429] Pid: 2139, comm: modprobe Not tainted 3.2.0-0.0.0.28.36b5ec9-default #2 [ 21.768253] Call Trace: [ 21.770838] [] lockdep_rcu_suspicious+0xcd/0x100 [ 21.777366] [] drain_mcelog_buffer+0x191/0x1b0 [ 21.783715] [] mce_register_decode_chain+0x18/0x20 [ 21.790430] [] i7core_register_mci+0x2fb/0x3e4 [i7core_edac] [ 21.798003] [] i7core_probe+0xd4/0x5c0 [i7core_edac] [ 21.804809] [] local_pci_probe+0x5b/0xe0 [ 21.810631] [] __pci_device_probe+0xd9/0xe0 [ 21.816650] [] ? get_device+0x14/0x20 [ 21.822178] [] pci_device_probe+0x36/0x60 [ 21.828061] [] really_probe+0x7a/0x2b0 [ 21.833676] [] driver_probe_device+0x63/0xc0 [ 21.839868] [] __driver_attach+0x9b/0xa0 [ 21.845718] [] ? driver_probe_device+0xc0/0xc0 [ 21.852027] [] bus_for_each_dev+0x68/0x90 [ 21.857876] [] driver_attach+0x1c/0x20 [ 21.863462] [] bus_add_driver+0x16d/0x2b0 [ 21.869377] [] driver_register+0x7c/0x160 [ 21.875220] [] __pci_register_driver+0x6a/0xf0 [ 21.881494] [] ? 0xffffffffa01fdfff [ 21.886846] [] i7core_init+0x47/0x1000 [i7core_edac] [ 21.893737] [] do_one_initcall+0x3e/0x180 [ 21.899670] [] sys_init_module+0xc5/0x220 [ 21.905542] [] system_call_fastpath+0x16/0x1b Fix this by using ACCESS_ONCE() instead of rcu_dereference_check_mce() over mcelog.next. Since the access to each entry is controlled by the ->finished field, ACCESS_ONCE() should work just fine. An rcu_dereference is unnecessary here. Signed-off-by: Srivatsa S. Bhat Suggested-by: Paul E. McKenney Cc: Tony Luck Signed-off-by: Borislav Petkov --- arch/x86/kernel/cpu/mcheck/mce.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index 5a11ae2e9e91..db590aff874c 100644 --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -191,7 +191,7 @@ static void drain_mcelog_buffer(void) { unsigned int next, i, prev = 0; - next = rcu_dereference_check_mce(mcelog.next); + next = ACCESS_ONCE(mcelog.next); do { struct mce *m; -- 2.39.2