Re: [PATCH v3 04/25] kcsan: Add core support for a subset of weak memory modeling
From: Paul E. McKenney
Date: Fri Dec 03 2021 - 18:42:27 EST
On Fri, Dec 03, 2021 at 01:08:56PM -0800, Paul E. McKenney wrote:
> On Fri, Dec 03, 2021 at 08:50:20AM -0800, Paul E. McKenney wrote:
> > On Fri, Dec 03, 2021 at 09:56:45AM +0100, Marco Elver wrote:
> > > On Tue, Nov 30, 2021 at 12:44PM +0100, Marco Elver wrote:
> > > [...]
> > > > v3:
> > > > * Remove kcsan_noinstr hackery, since we now try to avoid adding any
> > > > instrumentation to .noinstr.text in the first place.
> > > [...]
> > >
> > > I missed some cleanups after changes from v2 to v3 -- the below cleanup
> > > is missing.
> > >
> > > Full replacement patch attached.
> >
> > I pulled this into -rcu with the other patches from your v3 post, thank
> > you all!
>
> A few quick tests located the following:
>
> [ 0.635383] INFO: trying to register non-static key.
> [ 0.635804] The code is fine but needs lockdep annotation, or maybe
> [ 0.636194] you didn't initialize this object before use?
> [ 0.636194] turning off the locking correctness validator.
> [ 0.636194] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.16.0-rc1+ #3208
> [ 0.636194] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014
> [ 0.636194] Call Trace:
> [ 0.636194] <TASK>
> [ 0.636194] dump_stack_lvl+0x88/0xd8
> [ 0.636194] dump_stack+0x15/0x1b
> [ 0.636194] register_lock_class+0x6b3/0x840
> [ 0.636194] ? __this_cpu_preempt_check+0x1d/0x30
> [ 0.636194] __lock_acquire+0x81/0xee0
> [ 0.636194] ? lock_is_held_type+0xf1/0x160
> [ 0.636194] lock_acquire+0xce/0x230
> [ 0.636194] ? test_barrier+0x490/0x14c7
> [ 0.636194] ? lock_is_held_type+0xf1/0x160
> [ 0.636194] ? test_barrier+0x490/0x14c7
> [ 0.636194] _raw_spin_lock+0x36/0x50
> [ 0.636194] ? test_barrier+0x490/0x14c7
> [ 0.636194] ? kcsan_init+0xf/0x80
> [ 0.636194] test_barrier+0x490/0x14c7
> [ 0.636194] ? kcsan_debugfs_init+0x1f/0x1f
> [ 0.636194] kcsan_selftest+0x47/0xa0
> [ 0.636194] do_one_initcall+0x104/0x230
> [ 0.636194] ? rcu_read_lock_sched_held+0x5b/0xc0
> [ 0.636194] ? kernel_init+0x1c/0x200
> [ 0.636194] do_initcall_level+0xa5/0xb6
> [ 0.636194] do_initcalls+0x66/0x95
> [ 0.636194] do_basic_setup+0x1d/0x23
> [ 0.636194] kernel_init_freeable+0x254/0x2ed
> [ 0.636194] ? rest_init+0x290/0x290
> [ 0.636194] kernel_init+0x1c/0x200
> [ 0.636194] ? rest_init+0x290/0x290
> [ 0.636194] ret_from_fork+0x22/0x30
> [ 0.636194] </TASK>
>
> When running without the new patch series, this splat does not appear.
>
> Do I need a toolchain upgrade? I see the Clang 14.0 in the cover letter,
> but that seems to apply only to non-x86 architectures.
>
> $ clang-11 -v
> Ubuntu clang version 11.1.0-++20210805102428+1fdec59bffc1-1~exp1~20210805203044.169
And to further extend this bug report, the following patch suppresses
the error.
Thanx, Paul
------------------------------------------------------------------------
commit d157b802f05bd12cf40bef7a73ca6914b85c865e
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date: Fri Dec 3 15:35:29 2021 -0800
kcsan: selftest: Move test spinlock to static global
Running the TREE01 or TREE02 rcutorture scenarios results in the
following splat:
------------------------------------------------------------------------
INFO: trying to register non-static key.
The code is fine but needs lockdep annotation, or maybe
you didn't initialize this object before use?
turning off the locking correctness validator.
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.16.0-rc1+ #3208
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x88/0xd8
dump_stack+0x15/0x1b
register_lock_class+0x6b3/0x840
? __this_cpu_preempt_check+0x1d/0x30
__lock_acquire+0x81/0xee0
? lock_is_held_type+0xf1/0x160
lock_acquire+0xce/0x230
? test_barrier+0x490/0x14c7
? lock_is_held_type+0xf1/0x160
? test_barrier+0x490/0x14c7
_raw_spin_lock+0x36/0x50
? test_barrier+0x490/0x14c7
? kcsan_init+0xf/0x80
test_barrier+0x490/0x14c7
? kcsan_debugfs_init+0x1f/0x1f
kcsan_selftest+0x47/0xa0
do_one_initcall+0x104/0x230
? rcu_read_lock_sched_held+0x5b/0xc0
? kernel_init+0x1c/0x200
do_initcall_level+0xa5/0xb6
do_initcalls+0x66/0x95
do_basic_setup+0x1d/0x23
kernel_init_freeable+0x254/0x2ed
? rest_init+0x290/0x290
kernel_init+0x1c/0x200
? rest_init+0x290/0x290
ret_from_fork+0x22/0x30
</TASK>
------------------------------------------------------------------------
This appears to be due to this line of code in kernel/kcsan/selftest.c:
KCSAN_CHECK_READ_BARRIER(spin_unlock(&spinlock)), which operates on a
spinlock allocated on the stack. This shot-in-the-dark patch makes the
spinlock instead be a static global, which suppresses the above splat.
Fixes: 510b49b8d4c9 ("kcsan: selftest: Add test case to check memory barrier instrumentation")
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
diff --git a/kernel/kcsan/selftest.c b/kernel/kcsan/selftest.c
index 08c6b84b9ebed..05d772c9fe933 100644
--- a/kernel/kcsan/selftest.c
+++ b/kernel/kcsan/selftest.c
@@ -108,6 +108,8 @@ static bool __init test_matching_access(void)
return true;
}
+static DEFINE_SPINLOCK(test_barrier_spinlock);
+
/*
* Correct memory barrier instrumentation is critical to avoiding false
* positives: simple test to check at boot certain barriers are always properly
@@ -122,7 +124,6 @@ static bool __init test_barrier(void)
#endif
bool ret = true;
arch_spinlock_t arch_spinlock = __ARCH_SPIN_LOCK_UNLOCKED;
- DEFINE_SPINLOCK(spinlock);
atomic_t dummy;
long test_var;
@@ -172,8 +173,8 @@ static bool __init test_barrier(void)
KCSAN_CHECK_READ_BARRIER(clear_bit_unlock_is_negative_byte(0, &test_var));
arch_spin_lock(&arch_spinlock);
KCSAN_CHECK_READ_BARRIER(arch_spin_unlock(&arch_spinlock));
- spin_lock(&spinlock);
- KCSAN_CHECK_READ_BARRIER(spin_unlock(&spinlock));
+ spin_lock(&test_barrier_spinlock);
+ KCSAN_CHECK_READ_BARRIER(spin_unlock(&test_barrier_spinlock));
KCSAN_CHECK_WRITE_BARRIER(mb());
KCSAN_CHECK_WRITE_BARRIER(wmb());
@@ -202,8 +203,8 @@ static bool __init test_barrier(void)
KCSAN_CHECK_WRITE_BARRIER(clear_bit_unlock_is_negative_byte(0, &test_var));
arch_spin_lock(&arch_spinlock);
KCSAN_CHECK_WRITE_BARRIER(arch_spin_unlock(&arch_spinlock));
- spin_lock(&spinlock);
- KCSAN_CHECK_WRITE_BARRIER(spin_unlock(&spinlock));
+ spin_lock(&test_barrier_spinlock);
+ KCSAN_CHECK_WRITE_BARRIER(spin_unlock(&test_barrier_spinlock));
KCSAN_CHECK_RW_BARRIER(mb());
KCSAN_CHECK_RW_BARRIER(wmb());
@@ -235,8 +236,8 @@ static bool __init test_barrier(void)
KCSAN_CHECK_RW_BARRIER(clear_bit_unlock_is_negative_byte(0, &test_var));
arch_spin_lock(&arch_spinlock);
KCSAN_CHECK_RW_BARRIER(arch_spin_unlock(&arch_spinlock));
- spin_lock(&spinlock);
- KCSAN_CHECK_RW_BARRIER(spin_unlock(&spinlock));
+ spin_lock(&test_barrier_spinlock);
+ KCSAN_CHECK_RW_BARRIER(spin_unlock(&test_barrier_spinlock));
kcsan_nestable_atomic_end();