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Date: Tue, 2 Sep 2008 23:06:46 +0200
From: Luca Tettamanti <kronos.it@...il.com>
To: linux-kernel@...r.kernel.org
Cc: peterz@...radead.org, mingo@...hat.com
Subject: [2.6.27] early exception - lockdep related?
Hello,
I'm seeing an early exception (0e) - which seems related to lockdep - at
boot with many 2.6.27 kernels and I'm having troubles to track it down.
The strange thing is that it comes and goes with different kernel
versions, but a "bad" kernel consistently fails across reboots. It also
seems to be sensitive to the configuration (attached), at least in one
case the difference between a non-working kernel and a working one is
CONFIG_DEBUG enabled in the latter.
The address printed is inside the function __lock_acqurie:
in __lock_acquire (/home/kronos/src/linux-2.6.git/kernel/lockdep.c:727).
722
723 /*
724 * We can walk the hash lockfree, because the hash only
725 * grows, and we are careful when adding entries to the end:
726 */
727 list_for_each_entry(class, hash_head, hash_entry) {
728 if (class->key == key) {
729 WARN_ON_ONCE(class->name != lock->name);
730 return class;
731 }
And the disassembly (faulting address is 0xffffffff80253b66)
0xffffffff80253b00 <__lock_acquire+299>: shr $0x34,%rax
0xffffffff80253b04 <__lock_acquire+303>: shl $0x4,%rax
0xffffffff80253b08 <__lock_acquire+307>: lea -0x7f57e9b0(%rax),%rdx
0xffffffff80253b0f <__lock_acquire+314>: mov -0x7f57e9b0(%rax),%r13
0xffffffff80253b16 <__lock_acquire+321>: jmp 0xffffffff80253b66 <__lock_acquire+401>
0xffffffff80253b18 <__lock_acquire+323>: cmp %r8,0x20(%r13)
0xffffffff80253b1c <__lock_acquire+327>: jne 0xffffffff80253b63 <__lock_acquire+398>
0xffffffff80253b1e <__lock_acquire+329>: mov -0x90(%rbp),%r10
0xffffffff80253b25 <__lock_acquire+336>: mov 0x10(%r10),%r10
0xffffffff80253b29 <__lock_acquire+340>: cmp %r10,0x140(%r13)
0xffffffff80253b30 <__lock_acquire+347>: je 0xffffffff80253ea0 <__lock_acquire+1227>
0xffffffff80253b36 <__lock_acquire+353>: cmpl $0x0,0x51dc4f(%rip)
# 0xffffffff8077178c <__warned.16970>
0xffffffff80253b3d <__lock_acquire+360>: jne 0xffffffff80253ea0 <__lock_acquire+1227>
0xffffffff80253b43 <__lock_acquire+366>: mov $0x2d9,%esi
0xffffffff80253b48 <__lock_acquire+371>: mov $0xffffffff805691c7,%rdi
0xffffffff80253b4f <__lock_acquire+378>: callq 0xffffffff80232bae <warn_on_slowpath>
0xffffffff80253b54 <__lock_acquire+383>: movl $0x1,0x51dc2e(%rip)
# 0xffffffff8077178c <__warned.16970>
0xffffffff80253b5e <__lock_acquire+393>: jmpq 0xffffffff80253ea0 <__lock_acquire+1227>
0xffffffff80253b63 <__lock_acquire+398>: mov %rax,%r13
0xffffffff80253b66 <__lock_acquire+401>: mov 0x0(%r13),%rax <-- HERE
0xffffffff80253b6a <__lock_acquire+405>: cmp %rdx,%r13
0xffffffff80253b6d <__lock_acquire+408>: prefetcht0 (%rax)
0xffffffff80253b70 <__lock_acquire+411>: jne 0xffffffff80253b18 <__lock_acquire+323>
0xffffffff80253b72 <__lock_acquire+413>: callq 0xffffffff802513ba <static_obj>
0xffffffff80253b77 <__lock_acquire+418>: test %eax,%eax
0xffffffff80253b79 <__lock_acquire+420>: jne 0xffffffff80253ba8 <__lock_acquire+467>
0xffffffff80253b7b <__lock_acquire+422>: callq 0xffffffff8031db50 <debug_locks_off>
0xffffffff80253b80 <__lock_acquire+427>: mov $0xffffffff80569212,%rdi
0xffffffff80253b87 <__lock_acquire+434>: xor %eax,%eax
0xffffffff80253b89 <__lock_acquire+436>: callq 0xffffffff80487bd3 <printk>
0xffffffff80253b8e <__lock_acquire+441>: mov $0xffffffff8056923c,%rdi
0xffffffff80253b95 <__lock_acquire+448>: xor %eax,%eax
0xffffffff80253b97 <__lock_acquire+450>: callq 0xffffffff80487bd3 <printk>
0xffffffff80253b9c <__lock_acquire+455>: mov $0xffffffff8056926c,%rdi
0xffffffff80253ba3 <__lock_acquire+462>: jmpq 0xffffffff8025477c <__lock_acquire+3495>
0xffffffff80253ba8 <__lock_acquire+467>: mov -0x90(%rbp),%rdx
0xffffffff80253baf <__lock_acquire+474>: mov (%rdx),%rax
0xffffffff80253bb2 <__lock_acquire+477>: pushfq
0xffffffff80253bb3 <__lock_acquire+478>: popq -0x68(%rbp)
0xffffffff80253bb6 <__lock_acquire+481>: cli
0xffffffff80253bb7 <__lock_acquire+482>: mov $0x100,%ebx
0xffffffff80253bbc <__lock_acquire+487>: lock xadd %bx,0x51dbcb(%rip)
# 0xffffffff80771790 <lockdep_lock>
0xffffffff80253bc5 <__lock_acquire+496>: cmp %bh,%bl
0xffffffff80253bc7 <__lock_acquire+498>: je 0xffffffff80253bd3 <__lock_acquire+510>
0xffffffff80253bc9 <__lock_acquire+500>: pause
0xffffffff80253bcb <__lock_acquire+502>: mov 0x51dbbf(%rip),%bl
# 0xffffffff80771790 <lockdep_lock>
0xffffffff80253bd1 <__lock_acquire+508>: jmp 0xffffffff80253bc5 <__lock_acquire+496>
0xffffffff80253bd3 <__lock_acquire+510>: cmpl $0x0,0x397676(%rip)
# 0xffffffff805eb250 <debug_locks>
0xffffffff80253bda <__lock_acquire+517>: jne 0xffffffff80253beb <__lock_acquire+534>
0xffffffff80253bdc <__lock_acquire+519>: incb 0x51dbae(%rip) # 0xffffffff80771790 <lockdep_lock>
0xffffffff80253be2 <__lock_acquire+525>: pushq -0x68(%rbp)
0xffffffff80253be5 <__lock_acquire+528>: popfq
I actually tried to bisect it using an early working kernel and this first
(read: the first pull from Linus' tree that gave me a broken kernel). The
result is inconclusive, the commit pointed out was:
e5f363e358cf16e4ad13a6826e15088c5495efe9 is first bad commit
commit e5f363e358cf16e4ad13a6826e15088c5495efe9
Author: Ingo Molnar <mingo@...e.hu>
Date: Mon Aug 11 12:37:27 2008 +0200
lockdep: increase MAX_LOCKDEP_KEYS
certain configs produce:
[ 70.076229] BUG: MAX_LOCKDEP_KEYS too low!
[ 70.080230] turning off the locking correctness validator.
tune them up.
Signed-off-by: Ingo Molnar <mingo@...e.hu>
but reverting it didn't make any difference.
Is there any other action that I can take to debug this issue? Btw, do you
think that kgdb can be usefull? I can give it a try in the weekend...
Luca
--
Carpe diem, quam minimum credula postero. (Q. Horatius Flaccus)
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