[PATCH v7 30/38] s390/irqflags: Do not instrument arch_local_irq_*() with KMSAN

Ilya Leoshkevich
2024-06-21T11:37:58Z

Lockdep generates the following false positives with KMSAN on s390x:

[ 6.063666] DEBUG_LOCKS_WARN_ON(lockdep_hardirqs_enabled())
[ ...]
[ 6.577050] Call Trace:
[ 6.619637] [<000000000690d2de>] check_flags+0x1fe/0x210
[ 6.665411] ([<000000000690d2da>] check_flags+0x1fa/0x210)
[ 6.707478] [<00000000006cec1a>] lock_acquire+0x2ca/0xce0
[ 6.749959] [<00000000069820ea>] _raw_spin_lock_irqsave+0xea/0x190
[ 6.794912] [<00000000041fc988>] __stack_depot_save+0x218/0x5b0
[ 6.838420] [<000000000197affe>] __msan_poison_alloca+0xfe/0x1a0
[ 6.882985] [<0000000007c5827c>] start_kernel+0x70c/0xd50
[ 6.927454] [<0000000000100036>] startup_continue+0x36/0x40

Between trace_hardirqs_on() and `stosm __mask, 3` lockdep thinks that
interrupts are on, but on the CPU they are still off. KMSAN
instrumentation takes spinlocks, giving lockdep a chance to see and
complain about this discrepancy.

KMSAN instrumentation is inserted in order to poison the __mask
variable. Disable instrumentation in the respective functions. They are
very small and it's easy to see that no important metadata updates are
lost because of this.

Reviewed-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
arch/s390/include/asm/irqflags.h | 17 ++++++++++++++---
drivers/s390/char/sclp.c | 2 +-
2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/s390/include/asm/irqflags.h b/arch/s390/include/asm/irqflags.h
index 02427b205c11..bcab456dfb80 100644
--- a/arch/s390/include/asm/irqflags.h
+++ b/arch/s390/include/asm/irqflags.h
@@ -37,12 +37,18 @@ static __always_inline void __arch_local_irq_ssm(unsigned long flags)
asm volatile("ssm %0" : : "Q" (flags) : "memory");
}

-static __always_inline unsigned long arch_local_save_flags(void)
+#ifdef CONFIG_KMSAN
+#define arch_local_irq_attributes noinline notrace __no_sanitize_memory __maybe_unused
+#else
+#define arch_local_irq_attributes __always_inline
+#endif
+
+static arch_local_irq_attributes unsigned long arch_local_save_flags(void)
{
return __arch_local_irq_stnsm(0xff);
}

-static __always_inline unsigned long arch_local_irq_save(void)
+static arch_local_irq_attributes unsigned long arch_local_irq_save(void)
{
return __arch_local_irq_stnsm(0xfc);
}
@@ -52,7 +58,12 @@ static __always_inline void arch_local_irq_disable(void)
arch_local_irq_save();
}

-static __always_inline void arch_local_irq_enable(void)
+static arch_local_irq_attributes void arch_local_irq_enable_external(void)
+{
+ __arch_local_irq_stosm(0x01);
+}
+
+static arch_local_irq_attributes void arch_local_irq_enable(void)
{
__arch_local_irq_stosm(0x03);
}
diff --git a/drivers/s390/char/sclp.c b/drivers/s390/char/sclp.c
index d53ee34d398f..fb1d9949adca 100644
--- a/drivers/s390/char/sclp.c
+++ b/drivers/s390/char/sclp.c
@@ -736,7 +736,7 @@ sclp_sync_wait(void)
cr0_sync.val = cr0.val & ~CR0_IRQ_SUBCLASS_MASK;
cr0_sync.val |= 1UL << (63 - 54);
local_ctl_load(0, &cr0_sync);
- __arch_local_irq_stosm(0x01);
+ arch_local_irq_enable_external();
/* Loop until driver state indicates finished request */
while (sclp_running_state != sclp_running_state_idle) {
/* Check for expired request timer */
--
2.45.1