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Date: Tue, 28 Feb 2012 10:24:52 -0500 From: Sasha Levin <levinsasha928@...il.com> To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu> Cc: Dave Jones <davej@...hat.com>, linux-kernel <linux-kernel@...r.kernel.org> Subject: lockdep: Warning & NULL ptr deref Hi all, I was debugging an issue with Trinity leaving multiple zombie processes while running, so after letting trinity run for a bit to create a nice bunch of them, I wanted to get a sysrq-t trace. After running 'echo t > /proc/sysrq-trigger' I got the usual backtrace spew along with some scheduler debug info after that, but when lockdep tried printing lock data I got this: [ 359.241034] Showing all locks held in the system: [ 359.241034] 1 lock held by ksoftirqd/0/3: [ 359.241034] #0: [ 359.241034] ------------[ cut here ]------------ [ 359.241034] WARNING: at kernel/lockdep.c:146 print_lock+0xa0/0xb0() [ 359.241034] Pid: 2852, comm: sh Not tainted 3.3.0-rc5-next-20120227-sasha-dirty #26 [ 359.241034] Call Trace: [ 359.241034] [<ffffffff8110e1a0>] ? print_lock+0xa0/0xb0 [ 359.241034] [<ffffffff810ac705>] warn_slowpath_common+0x75/0xb0 [ 359.241034] [<ffffffff810ac805>] warn_slowpath_null+0x15/0x20 [ 359.241034] [<ffffffff8110e1a0>] print_lock+0xa0/0xb0 [ 359.241034] [<ffffffff8110e22e>] lockdep_print_held_locks+0x7e/0xf0 [ 359.241034] [<ffffffff81115220>] debug_show_all_locks+0x190/0x260 [ 359.241034] [<ffffffff810e47f7>] show_state_filter+0x177/0x220 [ 359.241034] [<ffffffff810e4680>] ? sched_show_task+0x190/0x190 [ 359.241034] [<ffffffff81971d4b>] sysrq_handle_showstate+0xb/0x10 [ 359.241034] [<ffffffff81972209>] __handle_sysrq+0x129/0x190 [ 359.241034] [<ffffffff81972270>] ? __handle_sysrq+0x190/0x190 [ 359.241034] [<ffffffff819722ba>] write_sysrq_trigger+0x4a/0x50 [ 359.241034] [<ffffffff81243c10>] proc_reg_write+0x80/0xc0 [ 359.241034] [<ffffffff811dba86>] vfs_write+0xc6/0x180 [ 359.241034] [<ffffffff811dbc2f>] sys_write+0x4f/0xa0 [ 359.241034] [<ffffffff826e4979>] system_call_fastpath+0x16/0x1b [ 359.241034] ---[ end trace 80d8165bc39af078 ]--- [ 359.241034] BUG: unable to handle kernel NULL pointer dereference at 0000000000000030 [ 359.241034] IP: [<ffffffff8110e03d>] get_usage_chars+0xd/0x80 [ 359.241034] PGD 3809b067 PUD 3809a067 PMD 0 [ 359.241034] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC [ 359.241034] CPU 1 [ 359.241034] Pid: 2852, comm: sh Tainted: G W 3.3.0-rc5-next-20120227-sasha-dirty #26 [ 359.241034] RIP: 0010:[<ffffffff8110e03d>] [<ffffffff8110e03d>] get_usage_chars+0xd/0x80 [ 359.241034] RSP: 0018:ffff880038825cf8 EFLAGS: 00010086 [ 359.241034] RAX: 0000000000000000 RBX: ffff880038825d18 RCX: 00000000297a2979 [ 359.241034] RDX: 0000000000000000 RSI: ffff880038825d18 RDI: 0000000000000000 [ 359.241034] RBP: ffff880038825d08 R08: 0000000000000000 R09: 0000000000000000 [ 359.241034] R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000000 [ 359.241034] R13: 0000000000000001 R14: ffff880038825da0 R15: ffff88003cc93000 [ 359.241034] FS: 00007ffd48666700(0000) GS:ffff88003e000000(0000) knlGS:0000000000000000 [ 359.241034] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 359.241034] CR2: 0000000000000030 CR3: 00000000392dc000 CR4: 00000000000406e0 [ 359.241034] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 359.241034] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 [ 359.241034] Process sh (pid: 2852, threadinfo ffff880038824000, task ffff88003cc93000) [ 359.241034] Stack: [ 359.241034] ffff880038825d18 0000000000000000 ffff880038825d38 ffffffff8110e0cf [ 359.241034] ffff880038825da0 ffff88003cc93000 ffff88003d2288e0 0000000000000000 [ 359.241034] ffff880038825d58 ffffffff8110e13e ffff88003d228000 0000000000000001 [ 359.241034] Call Trace: [ 359.241034] [<ffffffff8110e0cf>] print_lock_name+0x1f/0x50 [ 359.241034] [<ffffffff8110e13e>] print_lock+0x3e/0xb0 [ 359.241034] [<ffffffff8110e22e>] lockdep_print_held_locks+0x7e/0xf0 [ 359.241034] [<ffffffff81115220>] debug_show_all_locks+0x190/0x260 [ 359.241034] [<ffffffff810e47f7>] show_state_filter+0x177/0x220 [ 359.241034] [<ffffffff810e4680>] ? sched_show_task+0x190/0x190 [ 359.241034] [<ffffffff81971d4b>] sysrq_handle_showstate+0xb/0x10 [ 359.241034] [<ffffffff81972209>] __handle_sysrq+0x129/0x190 [ 359.241034] [<ffffffff81972270>] ? __handle_sysrq+0x190/0x190 [ 359.241034] [<ffffffff819722ba>] write_sysrq_trigger+0x4a/0x50 [ 359.241034] [<ffffffff81243c10>] proc_reg_write+0x80/0xc0 [ 359.241034] [<ffffffff811dba86>] vfs_write+0xc6/0x180 [ 359.241034] [<ffffffff811dbc2f>] sys_write+0x4f/0xa0 [ 359.241034] [<ffffffff826e4979>] system_call_fastpath+0x16/0x1b [ 359.241034] Code: b5 70 ff ff ff e8 34 fb ff ff 48 89 c6 eb ce e8 ea e7 f9 ff 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 54 49 89 fc 53 48 89 f3 <48> 8b 7f 30 31 f6 e8 c8 f0 ff ff be 01 00 00 00 88 03 49 8b 7c [ 359.241034] RIP [<ffffffff8110e03d>] get_usage_chars+0xd/0x80 [ 359.241034] RSP <ffff880038825cf8> [ 359.241034] CR2: 0000000000000030 [ 359.241034] ---[ end trace 80d8165bc39af079 ]--- I'll send some patches to prevent the NULL deref itself which happens since a chunk of the code in lockdep.c assumed hlock_class() can't return NULL. This won't fix the actual problem though, I'm not sure exactly how a held lock wouldn't have a class initialized to it. -- Sasha. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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