Re: [linux-next:master] [kasan] 187292be96: WARNING:suspicious_RCU_usage

[Neeraj upadhyay <neeraj.iitr10@gmail.com>]

Hi,

On Tue, Feb 20, 2024 at 1:33 PM Marco Elver <elver@google.com> wrote:
>
> On Tue, 20 Feb 2024 at 08:35, kernel test robot <oliver.sang@intel.com> wrote:
> >
> >
> >
> > Hello,
> >
> > we noticed this is a revert commit, below report is for an issue we observed
> > on this commit but not on its parent. just FYI.
> >
> > 113edefd366346b3 187292be96ae2be247807fac1c3
> > ---------------- ---------------------------
> >        fail:runs  %reproduction    fail:runs
> >            |             |             |
> >            :6          100%           6:6     dmesg.WARNING:suspicious_RCU_usage
> >
> >
> > kernel test robot noticed "WARNING:suspicious_RCU_usage" on:
> >
> > commit: 187292be96ae2be247807fac1c3a6d89a7cc2a84 ("kasan: revert eviction of stack traces in generic mode")
> > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
>
> This commit didn't touch rcutorture or the rcu subsystem in any way,
> so I currently don't understand how rcutorture would be affected.
> While stackdepot has started to use RCU, this already happened in a
> previous commit, and this particular commit actually reduced RCU usage
> (no more evictions and re-allocations of stacktraces).
>
> The only explanation I have is that it improved performance of a
> KASAN-enabled kernel (which the config here has enabled) so much that
> previously undiscovered issues have now become much more likely to
> occur.
>
> [+Cc rcu folks]
>
> > in testcase: rcutorture

The rcutorture test type executed here is busted_srcud (torture_type:
busted_srcud). The busted_srcud torture test creates bad reader critical
section usages - in this case the rcu reader lock acquired was not
srcu lock, which subsequently resulted in rcu_dereference_check() to
cause a splat due to srcu read lock not being held.

 So, this is expected behavior, and not a problem in either KASAN or RCU.



Thanks
Neeraj

> > version:
> > with following parameters:
> >
> >         runtime: 300s
> >         test: cpuhotplug
> >         torture_type: busted_srcud
> >
> >
> >
> > compiler: clang-17
> > test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> >
> > (please refer to attached dmesg/kmsg for entire log/backtrace)
> >
> >
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <oliver.sang@intel.com>
> > | Closes: https://lore.kernel.org/oe-lkp/202402201506.b7e4b9b6-oliver.sang@intel.com
> >
> >
> > [  292.513535][  T653] WARNING: suspicious RCU usage
> > [  292.514923][  T653] 6.8.0-rc4-00126-g187292be96ae #1 Not tainted
> > [  292.516369][  T653] -----------------------------
> > [  292.517743][  T653] kernel/rcu/rcutorture.c:1983 suspicious rcu_dereference_check() usage!
> > [  292.519310][  T653]
> > [  292.519310][  T653] other info that might help us debug this:
> > [  292.519310][  T653]
> > [  292.523130][  T653]
> > [  292.523130][  T653] rcu_scheduler_active = 2, debug_locks = 1
> > [  292.525644][  T653] no locks held by rcu_torture_rea/653.
> > [  292.526974][  T653]
> > [  292.526974][  T653] stack backtrace:
> > [  292.529271][  T653] CPU: 0 PID: 653 Comm: rcu_torture_rea Not tainted 6.8.0-rc4-00126-g187292be96ae #1
> > [  292.530780][  T653] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> > [  292.532329][  T653] Call Trace:
> > [  292.533524][  T653]  <TASK>
> > [ 292.534696][ T653] dump_stack_lvl (lib/dump_stack.c:?)
> > [ 292.535941][ T653] ? __cfi_dump_stack_lvl (lib/dump_stack.c:98)
> > [ 292.537221][ T653] ? lockdep_rcu_suspicious (kernel/locking/lockdep.c:6712)
> > [ 292.538523][ T653] rcu_torture_one_read (kernel/rcu/rcutorture.c:?) rcutorture
> > [ 292.539887][ T653] ? __cfi_lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4312)
> > [ 292.541226][ T653] ? rcu_torture_timer (kernel/rcu/rcutorture.c:1955) rcutorture
> > [ 292.542621][ T653] ? __cfi_rcu_torture_timer (kernel/rcu/rcutorture.c:2055) rcutorture
> > [ 292.544012][ T653] ? init_timer_key (include/linux/lockdep.h:135 include/linux/lockdep.h:142 include/linux/lockdep.h:148 kernel/time/timer.c:847 kernel/time/timer.c:867)
> > [ 292.545262][ T653] rcu_torture_reader (kernel/rcu/rcutorture.c:2093) rcutorture
> > [ 292.546579][ T653] ? __cfi_rcu_torture_reader (kernel/rcu/rcutorture.c:2076) rcutorture
> > [ 292.547872][ T653] ? __cfi__raw_spin_unlock_irqrestore (kernel/locking/spinlock.c:193)
> > [ 292.549108][ T653] ? __cfi_rcu_torture_timer (kernel/rcu/rcutorture.c:2055) rcutorture
> > [ 292.550341][ T653] ? __kthread_parkme (kernel/kthread.c:?)
> > [ 292.551425][ T653] ? __kthread_parkme (include/linux/instrumented.h:? include/asm-generic/bitops/instrumented-non-atomic.h:141 kernel/kthread.c:280)
> > [ 292.552489][ T653] kthread (kernel/kthread.c:390)
> > [ 292.553504][ T653] ? __cfi_rcu_torture_reader (kernel/rcu/rcutorture.c:2076) rcutorture
> > [ 292.554689][ T653] ? __cfi_kthread (kernel/kthread.c:341)
> > [ 292.555749][ T653] ret_from_fork (arch/x86/kernel/process.c:153)
> > [ 292.556792][ T653] ? __cfi_kthread (kernel/kthread.c:341)
> > [ 292.557852][ T653] ret_from_fork_asm (arch/x86/entry/entry_64.S:250)
> > [  292.558920][  T653]  </TASK>
> >
> >
> >
> > The kernel config and materials to reproduce are available at:
> > https://download.01.org/0day-ci/archive/20240220/202402201506.b7e4b9b6-oliver.sang@intel.com
> >
> >
> >
> > --
> > 0-DAY CI Kernel Test Service
> > https://github.com/intel/lkp-tests/wiki
> >
>