Re: [BUG] kvm: dereference srcu-protected pointer without srcu_read_lock() held

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Wed, Apr 21, 2010 at 11:17:22AM +0300, Avi Kivity wrote:
> On 04/21/2010 01:21 AM, Paul E. McKenney wrote:
> >
> >>Subject: [PATCH] kvm: add missing srcu_read_lock()
> >>
> >>I got this dmesg due to srcu_read_lock() is missing in
> >>kvm_mmu_notifier_release().
> >>
> >>===================================================
> >>[ INFO: suspicious rcu_dereference_check() usage. ]
> >>---------------------------------------------------
> >>arch/x86/kvm/x86.h:72 invoked rcu_dereference_check() without protection!
> >>
> >>other info that might help us debug this:
> >>
> >>
> >>rcu_scheduler_active = 1, debug_locks = 0
> >>2 locks held by qemu-system-x86/3100:
> >>  #0:  (rcu_read_lock){.+.+..}, at: [<ffffffff810d73dc>] __mmu_notifier_release+0x38/0xdf
> >>  #1:  (&(&kvm->mmu_lock)->rlock){+.+...}, at: [<ffffffffa0130a6a>] kvm_mmu_zap_all+0x21/0x5e [kvm]
> >>
> >>stack backtrace:
> >>Pid: 3100, comm: qemu-system-x86 Not tainted 2.6.34-rc3-22949-gbc8a97a-dirty #2
> >>Call Trace:
> >>  [<ffffffff8106afd9>] lockdep_rcu_dereference+0xaa/0xb3
> >>  [<ffffffffa0123a89>] unalias_gfn+0x56/0xab [kvm]
> >>  [<ffffffffa0119600>] gfn_to_memslot+0x16/0x25 [kvm]
> >>  [<ffffffffa012ffca>] gfn_to_rmap+0x17/0x6e [kvm]
> >>  [<ffffffffa01300c1>] rmap_remove+0xa0/0x19d [kvm]
> >>  [<ffffffffa0130649>] kvm_mmu_zap_page+0x109/0x34d [kvm]
> >>  [<ffffffffa0130a7e>] kvm_mmu_zap_all+0x35/0x5e [kvm]
> >>  [<ffffffffa0122870>] kvm_arch_flush_shadow+0x16/0x22 [kvm]
> >>  [<ffffffffa01189e0>] kvm_mmu_notifier_release+0x15/0x17 [kvm]
> >>  [<ffffffff810d742c>] __mmu_notifier_release+0x88/0xdf
> >>  [<ffffffff810d73dc>] ? __mmu_notifier_release+0x38/0xdf
> >>  [<ffffffff81040848>] ? exit_mm+0xe0/0x115
> >>  [<ffffffff810c2cb0>] exit_mmap+0x2c/0x17e
> >>  [<ffffffff8103c472>] mmput+0x2d/0xd4
> >>  [<ffffffff81040870>] exit_mm+0x108/0x115
> >>[...]
> >Queued, thank you, Lai!
> 
> Paul, I'd like to merge this via the kvm tree.

Very good, I have removed both of these kvm patches.  They are yours!  ;-)

							Thanx, Paul