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Date:   Thu, 26 May 2022 11:17:29 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     "Zhang, Qiang1" <qiang1.zhang@intel.com>
Cc:     "frederic@kernel.org" <frederic@kernel.org>,
        "rcu@vger.kernel.org" <rcu@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] rcu: Remove debug_object_active_state() from
 debug_rcu_head_queue/unqueue()
Message-ID: <20220526181729.GK1790663@paulmck-ThinkPad-P17-Gen-1>
Reply-To: paulmck@kernel.org
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On Wed, May 25, 2022 at 11:33:46PM +0000, Zhang, Qiang1 wrote:
> On Fri, May 13, 2022 at 01:03:19AM +0000, Zhang, Qiang1 wrote:
> > On Tue, May 10, 2022 at 11:07:48AM +0800, Zqiang wrote:
> > > Currently, the double call_rcu() detected only need call
> > > debug_object_activate() to check whether the rcu head object is 
> > > activated, the rcu head object usage state check is not necessary 
> > > and when call rcu_test_debug_objects() the
> > > debug_object_active_state() will output same callstack as 
> > > debug_object_activate(). so remove
> > > debug_object_active_state() to reduce the output of repeated callstack.
> > > 
> > > Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> > >
> > >Could you please post the output of the dmesg output of a failed check with your change?
> > >
> > 
> > Original output:
> > 
> > [    0.818279] ODEBUG: activate active (active state 1) object type: rcu_head hint: 0x0
> > [    0.818296] WARNING: CPU: 1 PID: 1 at lib/debugobjects.c:505 debug_print_object+0xd8/0xf0
> > [    0.818301] Modules linked in:
> > [    0.818304] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W         5.18.0-rc6-next-20220511-yoctodev-standard+ #75
> > [    0.818306] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> > [    0.818308] RIP: 0010:debug_print_object+0xd8/0xf0
> > [    0.818311] Code: dd 40 9e 03 9d e8 48 62 a2 ff 4d 89 f9 4d 89 e8 44 89 e1 48 8b 14 dd 40 9e 03 9d 4c 89 f6 48 c7 c7 c0 93 03 9d e8 f6 1a b1 00 <0f> f
> > [    0.818313] RSP: 0000:ffff88810033fad0 EFLAGS: 00010082
> > [    0.818315] RAX: 0000000000000000 RBX: 0000000000000003 RCX: 0000000000000000
> > [    0.818317] RDX: 0000000000000002 RSI: 0000000000000004 RDI: ffffed1020067f4c
> > [    0.818319] RBP: ffff88810033fb00 R08: ffffffff9b50d898 R09: fffffbfff3bf5c6d
> > [    0.818320] R10: 0000000000000003 R11: fffffbfff3bf5c6c R12: 0000000000000001
> > [    0.818322] R13: ffffffff9ce769a0 R14: ffffffff9d039a80 R15: 0000000000000000
> > [    0.818324] FS:  0000000000000000(0000) GS:ffff888158880000(0000) knlGS:0000000000000000
> > [    0.818327] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [    0.818329] CR2: 0000000000000000 CR3: 000000017600e000 CR4: 00000000001506e0
> > [    0.818330] Call Trace:
> > [    0.818331]  <TASK>
> > [    0.818333]  debug_object_activate+0x2b8/0x300
> > [    0.818336]  ? debug_object_assert_init+0x220/0x220
> > [    0.818340]  ? __kasan_check_write+0x14/0x20
> > [    0.818343]  call_rcu+0x98/0x1110
> > [    0.818347]  ? vprintk+0x4c/0x60
> > [    0.818350]  ? rcu_torture_fwd_cb_hist.cold+0xe9/0xe9
> > [    0.818354]  ? strict_work_handler+0x70/0x70
> > [    0.818357]  rcu_torture_init+0x18be/0x199e
> > [    0.818361]  ? srcu_init+0x133/0x133
> > [    0.818364]  ? __mutex_unlock_slowpath.isra.0+0x270/0x270
> > [    0.818368]  ? rcu_torture_barrier1cb+0x40/0x40
> > [    0.818371]  ? rcu_torture_barrier1cb+0x40/0x40
> > [    0.818374]  ? srcu_init+0x133/0x133
> > [    0.818377]  do_one_initcall+0xb3/0x300
> > [    0.818380]  ? initcall_blacklisted+0x150/0x150
> > [    0.818382]  ? parameq+0x70/0x90
> > [    0.818385]  ? __kasan_check_read+0x11/0x20
> > [    0.818389]  kernel_init_freeable+0x2b2/0x310
> > [    0.818392]  ? rest_init+0xf0/0xf0
> > [    0.818396]  kernel_init+0x1e/0x140
> > [    0.818399]  ret_from_fork+0x22/0x30
> > [    0.818402]  </TASK>
> > [    0.818403] ---[ end trace 0000000000000000 ]---
> > [    0.818405] ------------[ cut here ]------------
> > [    0.818405] ODEBUG: active_state active (active state 1) object type: rcu_head hint: 0x0
> > [    0.818421] WARNING: CPU: 1 PID: 1 at lib/debugobjects.c:505 debug_print_object+0xd8/0xf0
> > [    0.818424] Modules linked in:
> > [    0.818426] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W         5.18.0-rc6-next-20220511-yoctodev-standard+ #75
> > [    0.818428] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> > [    0.818430] RIP: 0010:debug_print_object+0xd8/0xf0
> > [    0.818432] Code: dd 40 9e 03 9d e8 48 62 a2 ff 4d 89 f9 4d 89 e8 44 89 e1 48 8b 14 dd 40 9e 03 9d 4c 89 f6 48 c7 c7 c0 93 03 9d e8 f6 1a b1 00 <0f> f
> > [    0.818435] RSP: 0000:ffff88810033fac0 EFLAGS: 00010086
> > [    0.818437] RAX: 0000000000000000 RBX: 0000000000000003 RCX: 0000000000000000
> > [    0.818438] RDX: 0000000000000002 RSI: 0000000000000004 RDI: ffffed1020067f4a
> > [    0.818440] RBP: ffff88810033faf0 R08: ffffffff9b50d898 R09: fffffbfff3bf5c6d
> > [    0.818441] R10: 0000000000000003 R11: fffffbfff3bf5c6c R12: 0000000000000001
> > [    0.818443] R13: ffffffff9ce769a0 R14: ffffffff9d039820 R15: 0000000000000000
> > [    0.818445] FS:  0000000000000000(0000) GS:ffff888158880000(0000) knlGS:0000000000000000
> > [    0.818448] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [    0.818449] CR2: 0000000000000000 CR3: 000000017600e000 CR4: 00000000001506e0
> > [    0.818451] Call Trace:
> > [    0.818452]  <TASK>
> > [    0.818453]  debug_object_active_state+0x1d6/0x210
> > [    0.818456]  ? debug_object_deactivate+0x210/0x210
> > [    0.818460]  ? __kasan_check_write+0x14/0x20
> > [    0.818464]  call_rcu+0xb7/0x1110
> > [    0.818466]  ? vprintk+0x4c/0x60
> > [    0.818469]  ? rcu_torture_fwd_cb_hist.cold+0xe9/0xe9
> > [    0.818472]  ? strict_work_handler+0x70/0x70
> > [    0.818476]  rcu_torture_init+0x18be/0x199e
> > [    0.818479]  ? srcu_init+0x133/0x133
> > [    0.818482]  ? __mutex_unlock_slowpath.isra.0+0x270/0x270
> > [    0.818486]  ? rcu_torture_barrier1cb+0x40/0x40
> > [    0.818489]  ? rcu_torture_barrier1cb+0x40/0x40
> > [    0.818492]  ? srcu_init+0x133/0x133
> > [    0.818495]  do_one_initcall+0xb3/0x300
> > [    0.818497]  ? initcall_blacklisted+0x150/0x150
> > [    0.818500]  ? parameq+0x70/0x90
> > [    0.818503]  ? __kasan_check_read+0x11/0x20
> > [    0.818507]  kernel_init_freeable+0x2b2/0x310
> > [    0.818510]  ? rest_init+0xf0/0xf0
> > [    0.818513]  kernel_init+0x1e/0x140
> > [    0.818515]  ret_from_fork+0x22/0x30
> > [    0.818519]  </TASK>
> > [    0.818520] ---[ end trace 0000000000000000 ]---
> > [    0.818521] rcu: call_rcu(): Double-freed CB 00000000e2817fcb->rcu_torture_leak_cb+0x0/0x10()!!!   non-slab/vmalloc memory
> > 
> > 
> > After apply this patch:
> > 
> > [    0.647048] ODEBUG: activate active (active state 0) object type: rcu_head hint: 0x0
> > [    0.647068] WARNING: CPU: 1 PID: 1 at lib/debugobjects.c:505 debug_print_object+0xd8/0xf0
> > [    0.647073] Modules linked in:
> > [    0.647075] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W         5.18.0-rc6-next-20220511-yoctodev-standard+ #77
> > [    0.647078] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> > [    0.647080] RIP: 0010:debug_print_object+0xd8/0xf0
> > [    0.647083] Code: dd 80 9d 43 a2 e8 38 62 a2 ff 4d 89 f9 4d 89 e8 44 89 e1 48 8b 14 dd 80 9d 43 a2 4c 89 f6 48 c7 c7 00 93 43 a2 e8 f6 1a b1 00 <0f> 0b 83 05 7b 62f
> > [    0.647085] RSP: 0000:ffff88810033fad0 EFLAGS: 00010082
> > [    0.647088] RAX: 0000000000000000 RBX: 0000000000000003 RCX: 0000000000000000
> > [    0.647090] RDX: 0000000000000002 RSI: 0000000000000004 RDI: ffffed1020067f4c
> > [    0.647091] RBP: ffff88810033fb00 R08: ffffffffa090d898 R09: fffffbfff467586d
> > [    0.647093] R10: 0000000000000003 R11: fffffbfff467586c R12: 0000000000000000
> > [    0.647095] R13: ffffffffa22769a0 R14: ffffffffa24399c0 R15: 0000000000000000
> > [    0.647097] FS:  0000000000000000(0000) GS:ffff88815b880000(0000) knlGS:0000000000000000
> > [    0.647100] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [    0.647102] CR2: 0000000000000000 CR3: 000000002f20e000 CR4: 00000000001506e0
> > [    0.647104] Call Trace:
> > [    0.647104]  <TASK>
> > [    0.647106]  debug_object_activate+0x2b8/0x300
> > [    0.647110]  ? debug_object_assert_init+0x220/0x220
> > [    0.647114]  ? __kasan_check_write+0x14/0x20
> > [    0.647118]  call_rcu+0x98/0x1100
> > [    0.647121]  ? vprintk+0x4c/0x60
> > [    0.647125]  ? rcu_torture_fwd_cb_hist.cold+0xe9/0xe9
> > [    0.647129]  ? strict_work_handler+0x50/0x50
> > [    0.647133]  rcu_torture_init+0x18be/0x199e
> > [    0.647136]  ? srcu_init+0x133/0x133
> > [    0.647140]  ? __mutex_unlock_slowpath.isra.0+0x270/0x270
> > [    0.647144]  ? rcu_torture_barrier1cb+0x40/0x40
> > [    0.647148]  ? rcu_torture_barrier1cb+0x40/0x40
> > [    0.647151]  ? srcu_init+0x133/0x133
> > [    0.647155]  do_one_initcall+0xb3/0x300
> > [    0.647157]  ? initcall_blacklisted+0x150/0x150
> > [    0.647160]  ? parameq+0x70/0x90
> > [    0.647164]  ? __kasan_check_read+0x11/0x20
> > [    0.647167]  kernel_init_freeable+0x2b2/0x310
> > [    0.647171]  ? rest_init+0xf0/0xf0
> > [    0.647174]  kernel_init+0x1e/0x140
> > [    0.647177]  ret_from_fork+0x22/0x30
> > [    0.647181]  </TASK>
> > [    0.647182] ---[ end trace 0000000000000000 ]---
> > [    0.647184] rcu: call_rcu(): Double-freed CB 000000009a684b70->rcu_torture_leak_cb+0x0/0x10()!!!   non-slab/vmalloc memory
> 
> >Very good, and thank you!
> >
> >Now suppose that someone passes a pointer to call_rcu(), but then invokes kfree() on that same object before the grace period ends.
> >Is the offending kfree() flagged?	
> >
> >If the CONFIG_DEBUG_OBJECTS_FREE is enabled, the debug_check_no_obj_freed() will check wether the object is activated in kfree() If is activated, also output callstack.
> >
> >__debug_check_no_obj_freed()
> >{........
> >	switch (obj->state) {
> >	case ODEBUG_STATE_ACTIVE:
> >	 	descr = obj->descr;
> >		state = obj->state;
> >		_spin_unlock_irqrestore(&db->lock, flags);
> >		debug_print_object(obj, "free");
> >	}
> >.........
> >}
> >
> >Hi Paul
> >
> >The __debug_check_no_obj_freed() only check obj->state,  don't care obj->astate, the debug_object_active_state() is not necessary.  If CONFIG_DEBUG_OBJECTS_FREE is not enabled, the kfree() will directly release it without check obj state.
> >
> >Any thoughts?
> >
> >Thanks,
> >Zqiang 
> 
> Hi Paul 
> 
> Sorry to bother you again, I think this change is still meaningful, or there is something I don't konw 
> if I can give you some suggestions, I will be happy to accept.

My concern with this patch is that there might be some odd scenario
somewhere in which valuable debugging information is lost.  Unfortunately,
I haven't had time to fully explore the space of possible sequences of
double-free and use-after-free bugs.

It -might- be OK, but I cannot prove it.  Thoughts?

							Thanx, Paul

> Thanks
> Zqiang
> 
> 
> >Thanks,
> >Zqiang
> 
> >
> >							Thanx, Paul
> 
> > Thanks,
> > Zqiang
> > 
> > 
> > 
> > >							Thanx, Paul
> > >
> > > ---
> > >  kernel/rcu/rcu.h | 13 +------------
> > >  1 file changed, 1 insertion(+), 12 deletions(-)
> > > 
> > > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index
> > > 15b96f990774..0604ecd16627 100644
> > > --- a/kernel/rcu/rcu.h
> > > +++ b/kernel/rcu/rcu.h
> > > @@ -179,27 +179,16 @@ static inline unsigned long rcu_seq_diff(unsigned long new, unsigned long old)
> > >   */
> > >  
> > >  #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
> > > -# define STATE_RCU_HEAD_READY	0
> > > -# define STATE_RCU_HEAD_QUEUED	1
> > >  
> > >  extern const struct debug_obj_descr rcuhead_debug_descr;
> > >  
> > >  static inline int debug_rcu_head_queue(struct rcu_head *head)  {
> > > -	int r1;
> > > -
> > > -	r1 = debug_object_activate(head, &rcuhead_debug_descr);
> > > -	debug_object_active_state(head, &rcuhead_debug_descr,
> > > -				  STATE_RCU_HEAD_READY,
> > > -				  STATE_RCU_HEAD_QUEUED);
> > > -	return r1;
> > > +	return debug_object_activate(head, &rcuhead_debug_descr);
> > >  }
> > >  
> > >  static inline void debug_rcu_head_unqueue(struct rcu_head *head)  {
> > > -	debug_object_active_state(head, &rcuhead_debug_descr,
> > > -				  STATE_RCU_HEAD_QUEUED,
> > > -				  STATE_RCU_HEAD_READY);
> > >  	debug_object_deactivate(head, &rcuhead_debug_descr);  }
> > >  #else	/* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
> > > --
> > > 2.25.1
> > >