We generally expect local_irq_save() and local_irq_restore() to be paired and sanely nested, and so local_irq_restore() expects to be called with irqs disabled. Thus, within local_irq_restore() we only trace irq flag changes when unmasking irqs.
This means that a sequence such as: | local_irq_disable(); | local_irq_save(flags); | local_irq_enable(); | local_irq_restore(flags); ... is liable to break things, as the local_irq_restore() would mask irqs without tracing this change. Similar problems may exist for architectures whose arch_irq_restore() function depends on being called with irqs disabled. We don't consider such sequences to be a good idea, so let's define those as forbidden, and add tooling to detect such broken cases. This patch adds debug code to WARN() when raw_local_irq_restore() is called with irqs enabled. As raw_local_irq_restore() is expected to pair with raw_local_irq_save(), it should never be called with irqs enabled. To avoid the possibility of circular header dependencies between irqflags.h and bug.h, the warning is handled in a separate C file. The new code is all conditional on a new CONFIG_DEBUG_IRQFLAGS symbol which is independent of CONFIG_TRACE_IRQFLAGS. As noted above such cases will confuse lockdep, so CONFIG_DEBUG_LOCKDEP now selects CONFIG_DEBUG_IRQFLAGS. Signed-off-by: Mark Rutland <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Juergen Gross <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> --- include/linux/irqflags.h | 12 ++++++++++++ kernel/locking/Makefile | 1 + kernel/locking/irqflag-debug.c | 11 +++++++++++ lib/Kconfig.debug | 8 ++++++++ 4 files changed, 32 insertions(+) create mode 100644 kernel/locking/irqflag-debug.c Since v1 [1]: * Remove per-instance bool in favour of a single WARN_ONCE() * Move check into raw_local_irq_restore() * Update Kconfig text and cover [1] https://lore.kernel.org/r/[email protected] Mark. diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h index 8de0e1373de7..600c10da321a 100644 --- a/include/linux/irqflags.h +++ b/include/linux/irqflags.h @@ -149,6 +149,17 @@ do { \ # define start_critical_timings() do { } while (0) #endif +#ifdef CONFIG_DEBUG_IRQFLAGS +extern void warn_bogus_irq_restore(void); +#define raw_check_bogus_irq_restore() \ + do { \ + if (unlikely(!arch_irqs_disabled())) \ + warn_bogus_irq_restore(); \ + } while (0) +#else +#define raw_check_bogus_irq_restore() do { } while (0) +#endif + /* * Wrap the arch provided IRQ routines to provide appropriate checks. */ @@ -162,6 +173,7 @@ do { \ #define raw_local_irq_restore(flags) \ do { \ typecheck(unsigned long, flags); \ + raw_check_bogus_irq_restore(); \ arch_local_irq_restore(flags); \ } while (0) #define raw_local_save_flags(flags) \ diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile index 6d11cfb9b41f..8838f1d7c4a2 100644 --- a/kernel/locking/Makefile +++ b/kernel/locking/Makefile @@ -15,6 +15,7 @@ CFLAGS_REMOVE_mutex-debug.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_rtmutex-debug.o = $(CC_FLAGS_FTRACE) endif +obj-$(CONFIG_DEBUG_IRQFLAGS) += irqflag-debug.o obj-$(CONFIG_DEBUG_MUTEXES) += mutex-debug.o obj-$(CONFIG_LOCKDEP) += lockdep.o ifeq ($(CONFIG_PROC_FS),y) diff --git a/kernel/locking/irqflag-debug.c b/kernel/locking/irqflag-debug.c new file mode 100644 index 000000000000..9603d207a4ca --- /dev/null +++ b/kernel/locking/irqflag-debug.c @@ -0,0 +1,11 @@ +// SPDX-License-Identifier: GPL-2.0-only + +#include <linux/bug.h> +#include <linux/export.h> +#include <linux/irqflags.h> + +void warn_bogus_irq_restore(void) +{ + WARN_ONCE(1, "raw_local_irq_restore() called with IRQs enabled\n"); +} +EXPORT_SYMBOL(warn_bogus_irq_restore); diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 7937265ef879..5ea0c1773b0a 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1335,6 +1335,7 @@ config LOCKDEP_SMALL config DEBUG_LOCKDEP bool "Lock dependency engine debugging" depends on DEBUG_KERNEL && LOCKDEP + select DEBUG_IRQFLAGS help If you say Y here, the lock dependency engine will do additional runtime checks to debug itself, at the price @@ -1423,6 +1424,13 @@ config TRACE_IRQFLAGS_NMI depends on TRACE_IRQFLAGS depends on TRACE_IRQFLAGS_NMI_SUPPORT +config DEBUG_IRQFLAGS + bool "Debug IRQ flag manipulation" + help + Enables checks for potentially unsafe enabling or disabling of + interrupts, such as calling raw_local_irq_restore() when interrupts + are enabled. + config STACKTRACE bool "Stack backtrace support" depends on STACKTRACE_SUPPORT -- 2.11.0
