Messages in this thread | | | Date | Mon, 5 Jan 2009 11:36:02 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [BUG] NULL pointer deref with rcutorture |
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On Mon, Jan 05, 2009 at 07:56:55PM +0100, Eric Sesterhenn wrote: > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > > On Mon, Jan 05, 2009 at 01:14:09PM +0100, Eric Sesterhenn wrote: > > > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > > > > > > Could the popular rcu function be registered by rcutorture, but when > > > we remove the module the callback is no longer valid? I can compile > > > a kernel just fine and with other stress tests i did not see any oops so > > > far. > > > > One approach would be to print out the address of rcutorture's RCU > > callbacks at rcutorture module initialization time (in rcu_torture_init() > > in kernel/rcutorture.c). The two callbacks are rcu_torture_cb() and > > rcu_bh_torture_wakeme_after_cb(). Unless you are specifying the > > "torture_type" parameter to rcutorture, only the first one should be in > > use. > > with a printk(KERN_ERR "rcu_torture_cb: %p rcu_bh_torture_wakeme_after_cb: > %p\n", rcu_torture_cb, rcu_bh_torture_wakeme_after_cb);
Cool!
> [ 65.135468] rcu_torture_cb: d0af7d1b rcu_bh_torture_wakeme_after_cb: > d0af7bec > [ 65.135672] rcu-torture:--- Start of test: nreaders=2 nfakewriters=4 > stat_interval=0 verbose=0 test_no_idle_hz=0 shuffle_interval=3 stutter=5 > irqreader=1 > [ 71.171603] BUG: unable to handle kernel NULL pointer dereference at > (null) > [ 71.171954] IP: [<d0af7a0f>] 0xd0af7a0f > [ 71.192822] *pde = 00000000 > [ 71.196513] Oops: 0002 [#1] PREEMPT DEBUG_PAGEALLOC > [ 71.196826] last sysfs file: /sys/block/ram9/range > [ 71.197010] Modules linked in: [last unloaded: rcutorture] > [ 71.197010] > [ 71.197010] Pid: 4861, comm: rcu_torture_wri Tainted: G W > (2.6.28-05716-gfe0bdec-dirty #171) System Name > [ 71.197010] EIP: 0060:[<d0af7a0f>] EFLAGS: 00010282 CPU: 0 > [ 71.197010] EIP is at 0xd0af7a0f > [ 71.197010] EAX: 00000000 EBX: d0afbc20 ECX: c04f5cef EDX: c98abf7c > [ 71.197010] ESI: d0af7df0 EDI: 00000000 EBP: c98abfc4 ESP: c98abfc4 > [ 71.197010] DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068 > [ 71.197010] Process rcu_torture_wri (pid: 4861, ti=c98ab000 > task=c9890d00 task.ti=c98ab000) > [ 71.197010] Stack: > [ 71.197010] c98abfd0 d0af7eeb 00000000 c98abfe0 c0137364 c0137326 > 00000000 00000000 > [ 71.197010] c0103643 c981fea4 00000000 00000000 00000000 00000000 > 00000000 > [ 71.197010] Call Trace: > [ 71.197010] [<c0137364>] ? kthread+0x3e/0x66 > [ 71.197010] [<c0137326>] ? kthread+0x0/0x66 > [ 71.197010] [<c0103643>] ? kernel_thread_helper+0x7/0x10 > [ 71.197010] Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > 00 00 <00> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > [ 71.197010] EIP: [<d0af7a0f>] 0xd0af7a0f SS:ESP 0068:c98abfc4 > [ 71.301103] ---[ end trace 4eaa2a86a8e2da22 ]--- > > If i interpret this correctly, this corresponds to > > 000009e8 <rcu_stutter_wait>: > 9e8: 55 push %ebp > 9e9: 89 e5 mov %esp,%ebp > 9eb: e8 fc ff ff ff call 9ec <rcu_stutter_wait+0x4>
Wow!!! Am I reading this correctly? Does the above "call" instruction -really- call one byte into itself? That is what the hex for the x86 instruction -looks- like it is doing, but I cannot see what would have possessed the compiler to generate this code.
When I compile on a 32-bit x86 machine, I don't see the above "call" instruction. Other than that, the code I see looks consistent.
> 9f0: eb 1d jmp a0f <rcu_stutter_wait+0x27> > 9f2: 83 3d 00 00 00 00 00 cmpl $0x0,0x0 > 9f9: b8 01 00 00 00 mov $0x1,%eax > 9fe: 75 0a jne a0a <rcu_stutter_wait+0x22> > a00: b8 e8 03 00 00 mov $0x3e8,%eax > a05: e8 fc ff ff ff call a06 <rcu_stutter_wait+0x1e> > a0a: e8 fc ff ff ff call a0b <rcu_stutter_wait+0x23> > a0f: 83 3d 6c 00 00 00 00 cmpl $0x0,0x6c > ^---------- this line
This looks like the first test in the "while" loop.
> a16: 75 09 jne a21 <rcu_stutter_wait+0x39> > a18: 83 3d 00 00 00 00 00 cmpl $0x0,0x0 > a1f: 75 09 jne a2a <rcu_stutter_wait+0x42> > a21: 83 3d 50 1a 00 00 00 cmpl $0x0,0x1a50 > a28: 74 c8 je 9f2 <rcu_stutter_wait+0xa> > a2a: 5d pop %ebp > a2b: c3 ret
The corresponding C code is as follows:
static void rcu_stutter_wait(void) { while ((stutter_pause_test || !rcutorture_runnable) && !fullstop) { if (rcutorture_runnable) schedule_timeout_interruptible(1); else schedule_timeout_interruptible(round_jiffies_relative(HZ)); } }
I don't see much opportunity for a page fault here... This is the binary I get when I compile it, though not as a module:
0000085a <rcu_stutter_wait>: 85a: 55 push %ebp 85b: 89 e5 mov %esp,%ebp 85d: eb 1d jmp 87c <rcu_stutter_wait+0x22> 85f: 83 3d 00 00 00 00 00 cmpl $0x0,0x0 866: b8 01 00 00 00 mov $0x1,%eax 86b: 75 0a jne 877 <rcu_stutter_wait+0x1d> 86d: b8 e8 03 00 00 mov $0x3e8,%eax 872: e8 fc ff ff ff call 873 <rcu_stutter_wait+0x19> 877: e8 fc ff ff ff call 878 <rcu_stutter_wait+0x1e> 87c: 83 3d 14 00 00 00 00 cmpl $0x0,0x14 883: 75 09 jne 88e <rcu_stutter_wait+0x34> 885: 83 3d 00 00 00 00 00 cmpl $0x0,0x0 88c: 75 09 jne 897 <rcu_stutter_wait+0x3d> 88e: 83 3d 08 1a 00 00 00 cmpl $0x0,0x1a08 895: 74 c8 je 85f <rcu_stutter_wait+0x5> 897: 5d pop %ebp 898: c3 ret
I confess, I am confused!!!
Thanx, Paul
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