If two (or more) unknown NMIs arrive on different CPUs, there is a large chance both CPUs will wind up inside panic(). This is fine, unless you want to enter KDB - KDB cannot round up all CPUs, because some of them are stuck inside panic_smp_self_stop with NMI latched. This is easy to replicate with QEMU. Boot with -smp 4 and send NMI using the monitor.
Solution for this - attempt to enter panic() from NMI handler. If panic() is already active in the system, just exit out of the NMI handler. This lets KDB round up CPUs. Signed-off-by: Andrei Warkentin <[email protected]> --- arch/x86/kernel/nmi.c | 6 ++-- include/linux/kernel.h | 1 + kernel/panic.c | 82 +++++++++++++++++++++++++++++++++++++----------- 3 files changed, 67 insertions(+), 22 deletions(-) diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 47acaf3..9e6a69a 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -227,7 +227,7 @@ pci_serr_error(unsigned char reason, struct pt_regs *regs) #endif if (panic_on_unrecovered_nmi) - panic("NMI: Not continuing"); + try_panic("NMI: Not continuing"); pr_emerg("Dazed and confused, but trying to continue\n"); @@ -247,7 +247,7 @@ io_check_error(unsigned char reason, struct pt_regs *regs) show_registers(regs); if (panic_on_io_nmi) - panic("NMI IOCK error: Not continuing"); + try_panic("NMI IOCK error: Not continuing"); /* Re-enable the IOCK line, wait for a few seconds */ reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_IOCHK; @@ -297,7 +297,7 @@ unknown_nmi_error(unsigned char reason, struct pt_regs *regs) pr_emerg("Do you have a strange power saving mode enabled?\n"); if (unknown_nmi_panic || panic_on_unrecovered_nmi) - panic("NMI: Not continuing"); + try_panic("NMI: Not continuing"); pr_emerg("Dazed and confused, but trying to continue\n"); } diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 01ab0aa..82983f9 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -188,6 +188,7 @@ extern long (*panic_blink)(int state); __printf(1, 2) void panic(const char *fmt, ...) __noreturn __cold; +void try_panic(const char *fmt, ...) __cold; extern void oops_enter(void); extern void oops_exit(void); void print_oops_end_marker(void); diff --git a/kernel/panic.c b/kernel/panic.c index 80aed44..9c88b49 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -58,40 +58,26 @@ void __weak panic_smp_self_stop(void) cpu_relax(); } +static DEFINE_SPINLOCK(panic_lock); + /** - * panic - halt the system + * __panic - halt the system * @fmt: The text string to print + * @args: va_list associated with fmt * * Display a message, then perform cleanups. * * This function never returns. */ -void panic(const char *fmt, ...) +void __noreturn __cold __panic(const char *fmt, va_list args) { - static DEFINE_SPINLOCK(panic_lock); static char buf[1024]; - va_list args; long i, i_next = 0; int state = 0; - /* - * It's possible to come here directly from a panic-assertion and - * not have preempt disabled. Some functions called from here want - * preempt to be disabled. No point enabling it later though... - * - * Only one CPU is allowed to execute the panic code from here. For - * multiple parallel invocations of panic, all other CPUs either - * stop themself or will wait until they are stopped by the 1st CPU - * with smp_send_stop(). - */ - if (!spin_trylock(&panic_lock)) - panic_smp_self_stop(); - console_verbose(); bust_spinlocks(1); - va_start(args, fmt); vsnprintf(buf, sizeof(buf), fmt, args); - va_end(args); printk(KERN_EMERG "Kernel panic - not syncing: %s\n",buf); #ifdef CONFIG_DEBUG_BUGVERBOSE /* @@ -175,8 +161,66 @@ void panic(const char *fmt, ...) } } +/** + * panic - halt the system + * @fmt: The text string to print + * + * Display a message, then perform cleanups. + * + * This function never returns. + */ +void panic(const char *fmt, ...) +{ + va_list args; + + /* + * It's possible to come here directly from a panic-assertion and + * not have preempt disabled. Some functions called from here want + * preempt to be disabled. No point enabling it later though... + * + * Only one CPU is allowed to execute the panic code from here. For + * multiple parallel invocations of panic, all other CPUs either + * stop themself or will wait until they are stopped by the 1st CPU + * with smp_send_stop(). + */ + if (!spin_trylock(&panic_lock)) + panic_smp_self_stop(); + + va_start(args, fmt); + __panic(fmt, args); +} + EXPORT_SYMBOL(panic); +/** + * try_panic - halt the system, unless + * another panic is in progress + * @fmt: The text string to print + * + * Display a message, then perform cleanups. + * + * This function retuns if panic_lock is already taken. + * It is meant to be used in places which can be invoked + * concurrently on several CPUs, but where its undesired + * for the CPU to become wedged if it cannot take + * the panic lock - for example, doing so inside an + * NMI will prevent KDB from working if it's running + * due to an unknown broadcast NMI (won't be able to + * roundup using NMI, since the other CPU is spinning + * inside panic_smp_self_stop with NMI latched). + */ +void try_panic(const char *fmt, ...) +{ + va_list args; + + if (!spin_trylock(&panic_lock)) + return; + + va_start(args, fmt); + __panic(fmt, args); +} + +EXPORT_SYMBOL(try_panic); struct tnt { u8 bit; -- 1.7.9.2 ------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/ _______________________________________________ Kgdb-bugreport mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport
