On Tue, Mar 17, 2020 at 01:56:40PM -0400, Qian Cai wrote:
> It is safe to traverse mm->notifier_subscriptions->list either under
> SRCU read lock or mm->notifier_subscriptions->lock using
> hlist_for_each_entry_rcu(). Silence the PROVE_RCU_LIST false positives,
> for example,
>
> WARNING: suspicious RCU usage
> -----------------------------
> mm/mmu_notifier.c:484 RCU-list traversed in non-reader section!!
>
> other info that might help us debug this:
>
> rcu_scheduler_active = 2, debug_locks = 1
> 3 locks held by libvirtd/802:
> #0: ffff9321e3f58148 (&mm->mmap_sem#2){++++}, at: do_mprotect_pkey+0xe1/0x3e0
> #1: ffffffff91ae6160 (mmu_notifier_invalidate_range_start){+.+.}, at: change_p4d_range+0x5fa/0x800
> #2: ffffffff91ae6e08 (srcu){....}, at: __mmu_notifier_invalidate_range_start+0x178/0x460
>
> stack backtrace:
> CPU: 7 PID: 802 Comm: libvirtd Tainted: G I 5.6.0-rc6-next-20200317+ #2
> Hardware name: HP ProLiant BL460c Gen8, BIOS I31 11/02/2014
> Call Trace:
> dump_stack+0xa4/0xfe
> lockdep_rcu_suspicious+0xeb/0xf5
> __mmu_notifier_invalidate_range_start+0x3ff/0x460
> change_p4d_range+0x746/0x800
> change_protection+0x1df/0x300
> mprotect_fixup+0x245/0x3e0
> do_mprotect_pkey+0x23b/0x3e0
> __x64_sys_mprotect+0x51/0x70
> do_syscall_64+0x91/0xae8
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
>
> Signed-off-by: Qian Cai <cai@xxxxxx>
> ---
> mm/mmu_notifier.c | 27 ++++++++++++++++++---------
> 1 file changed, 18 insertions(+), 9 deletions(-)
Looks right to me
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
This was missed during testing because we don't run with
PROVE_RCU_LIST enabled
Jason
