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SubjectRe: [BUG] NULL pointer deref with rcutorture
On Mon, Jan 05, 2009 at 09:01:45PM +0100, Eric Sesterhenn wrote:
> hi,
>
> * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote:
> > On Mon, Jan 05, 2009 at 07:56:55PM +0100, Eric Sesterhenn wrote:
> > > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote:
> > > [ 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.
>
> Compiler is gcc version 4.2.4 (Ubuntu 4.2.4-1ubuntu3)

I am using 4.1.3, for whatever it is worth. (Ancient, I know!)

> > 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!!!
>
> on the other box with a different gcc version
>
> gcc version 4.3.2 (Ubuntu 4.3.2-1ubuntu11)
>
> d1902e90 is the start of rcu_stutter_wait
>
> [ 533.391719] d087e000 d1902e90
> [ 533.392294] 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
> [ 541.000139] BUG: unable to handle kernel paging request at d1902efd
> [ 541.000423] IP: [<d1902efd>] 0xd1902efd
> [ 541.000660] *pde = 0f08f067 *pte = 00000000
> [ 541.000867] Oops: 0000 [#1] DEBUG_PAGEALLOC
> [ 541.001126] last sysfs file: /sys/block/sda/size
> [ 541.001246] Modules linked in: nfsd exportfs nfs lockd nfs_acl auth_rpcgss sunrpc ipv6 fuse unix [last unloaded: rcutorture]
> [ 541.002235]
> [ 541.002334] Pid: 5292, comm: rcu_torture_wri Not tainted (2.6.28 #84)
> [ 541.002470] EIP: 0060:[<d1902efd>] EFLAGS: 00010296 CPU: 0
> [ 541.002598] EIP is at 0xd1902efd
> [ 541.002767] EAX: 00000000 EBX: d19073c0 ECX: 00000000 EDX: 00000000
> [ 541.002900] ESI: 0000000a EDI: 00000000 EBP: c7b63fb8 ESP: c7b63fb8
> [ 541.003033] DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
> [ 541.003160] Process rcu_torture_wri (pid: 5292, ti=c7b63000 task=c7b09710 task.ti=c7b63000)
> [ 541.003400] Stack:
> [ 541.003497] c7b63fd0 d19032c1 00000000 00000000 00000000 d1903200 c7b63fe0 c013d80a
> [ 541.004022] c013d7d0 00000000 00000000 c0103cf3 cef6ee70 00000000 00000000 00000000
> [ 541.004022] 00000201 000004b4
> [ 541.004022] Call Trace:
> [ 541.004022] [<c013d80a>] ? kthread+0x3a/0x70
> [ 541.004022] [<c013d7d0>] ? kthread+0x0/0x70
> [ 541.004022] [<c0103cf3>] ? kernel_thread_helper+0x7/0x14
> [ 541.004022] Code: Bad EIP value.
> [ 541.004022] EIP: [<d1902efd>] 0xd1902efd SS:ESP 0068:c7b63fb8
> [ 541.004022] ---[ end trace cb3b10c2bb94b4e3 ]---
>
>
> 00000e90 <rcu_stutter_wait>:
> e90: 55 push %ebp
> e91: 89 e5 mov %esp,%ebp
> e93: 90 nop
> e94: 8d 74 26 00 lea 0x0(%esi,%eiz,1),%esi
> e98: a1 98 00 00 00 mov 0x98,%eax
> e9d: 85 c0 test %eax,%eax
> e9f: 75 09 jne eaa <rcu_stutter_wait+0x1a>
> ea1: a1 00 00 00 00 mov 0x0,%eax
> ea6: 85 c0 test %eax,%eax
> ea8: 75 36 jne ee0 <rcu_stutter_wait+0x50>
> eaa: a1 88 1a 00 00 mov 0x1a88,%eax
> eaf: 85 c0 test %eax,%eax
> eb1: 75 2d jne ee0 <rcu_stutter_wait+0x50>
> eb3: 8b 15 00 00 00 00 mov 0x0,%edx
> eb9: 85 d2 test %edx,%edx
> ebb: 74 2b je ee8 <rcu_stutter_wait+0x58>
> ebd: b8 01 00 00 00 mov $0x1,%eax
> ec2: e8 fc ff ff ff call ec3 <rcu_stutter_wait+0x33>
> ec7: a1 98 00 00 00 mov 0x98,%eax
> ecc: 85 c0 test %eax,%eax
> ece: 74 d1 je ea1 <rcu_stutter_wait+0x11>
> ed0: a1 88 1a 00 00 mov 0x1a88,%eax
> ed5: 85 c0 test %eax,%eax
> ed7: 74 da je eb3 <rcu_stutter_wait+0x23>
> ed9: 8d b4 26 00 00 00 00 lea 0x0(%esi,%eiz,1),%esi
> ee0: 5d pop %ebp
> ee1: c3 ret
> ee2: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
> ee8: b8 fa 00 00 00 mov $0xfa,%eax
> eed: e8 fc ff ff ff call eee <rcu_stutter_wait+0x5e>

Here we are again calling one byte into the current instruction!!!

Or am I misinterpreting this code?

> ef2: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
> ef8: e8 fc ff ff ff call ef9 <rcu_stutter_wait+0x69>
> efd: 8d 76 00 lea 0x0(%esi),%esi
> ^------------- here
>
> This one looks more like it can explain a page fault

I don't understand why there are indirections in the assembly given the
C code for rcu_stutter_wait().

> f00: eb 96 jmp e98 <rcu_stutter_wait+0x8>
> f02: 8d b4 26 00 00 00 00 lea 0x0(%esi,%eiz,1),%esi
> f09: 8d bc 27 00 00 00 00 lea 0x0(%edi,%eiz,1),%edi
>
> Greetings, Eric

Thanx, Paul


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