crash_smp_send_stop() is a special variant of smp_send_stop(). It is
used when crash_kexec_post_notifiers are enabled. CPUs are stopped
but cpu_online_mask is not updated so that the original information is
visible in crashdump. See the commit 0ee59413c967c35a6dd ("x86/panic:
replace smp_send_stop() with kdump friendly version in panic path")
for more details.crash_smp_send_stop() uses NMI to stop the CPUs. Then logbuf_lock might stay locked but printk_bust_lock_safe() does not know that CPUs are stopped. Solution is to force logbuf_lock re-initialization from crash_smp_send_stop(). Note that x86 seems to be the only architecture that implements crash_smp_send_stop() and uses NMI at the same time. Other architectures could not guarantee that the CPUs were really stopped. Signed-off-by: Petr Mladek <[email protected]> --- arch/x86/kernel/crash.c | 6 +++++- include/linux/printk.h | 4 ++-- kernel/panic.c | 2 +- kernel/printk/printk_safe.c | 8 +++++--- 4 files changed, 13 insertions(+), 7 deletions(-) diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c index 2bf70a2fed90..9a497eb37bf7 100644 --- a/arch/x86/kernel/crash.c +++ b/arch/x86/kernel/crash.c @@ -99,7 +99,11 @@ static void kdump_nmi_callback(int cpu, struct pt_regs *regs) void kdump_nmi_shootdown_cpus(void) { nmi_shootdown_cpus(kdump_nmi_callback); - + /* + * CPUs are stopped but it is not visible via cpus_online + * bitmap. Bust logbuf_lock to make kmsg_dump() working. + */ + printk_bust_lock_safe(true); disable_local_APIC(); } diff --git a/include/linux/printk.h b/include/linux/printk.h index 4d15a0eda9c6..c050f1dafc32 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -202,7 +202,7 @@ __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...); void dump_stack_print_info(const char *log_lvl); void show_regs_print_info(const char *log_lvl); extern asmlinkage void dump_stack(void) __cold; -extern int printk_bust_lock_safe(void); +extern int printk_bust_lock_safe(bool kdump_smp_stop); extern void printk_safe_init(void); extern void printk_safe_flush(void); extern void printk_safe_flush_on_panic(void); @@ -270,7 +270,7 @@ static inline void dump_stack(void) { } -static inline int printk_bust_lock_safe(void) +static inline int printk_bust_lock_safe(bool kdump_smp_stop) { return 0; } diff --git a/kernel/panic.c b/kernel/panic.c index aa50cdb75022..54fae99e7a7e 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -274,7 +274,7 @@ void panic(const char *fmt, ...) atomic_notifier_call_chain(&panic_notifier_list, 0, buf); /* Call flush even twice. It tries harder with a single online CPU */ - printk_blocked = printk_bust_lock_safe(); + printk_blocked = printk_bust_lock_safe(false); if (!printk_blocked) { printk_safe_flush_on_panic(); kmsg_dump(KMSG_DUMP_PANIC); diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index 71d4b763f811..e26304277886 100644 --- a/kernel/printk/printk_safe.c +++ b/kernel/printk/printk_safe.c @@ -255,16 +255,18 @@ void printk_safe_flush(void) /** * printk_try_bust_lock - make printk log accessible when safe + * @kdump_smp_stop: true when called after kdump stopped CPUs via NMI + * but did not update the number of online CPUs. * * Return 0 when the log is accessible. Return -EWOULDBLOCK when * it is not safe and likely to cause a deadlock. */ -int printk_bust_lock_safe(void) +int printk_bust_lock_safe(bool kdump_smp_stop) { if (!raw_spin_is_locked(&logbuf_lock)) return 0; - if (num_online_cpus() == 1) { + if (num_online_cpus() == 1 || kdump_smp_stop) { debug_locks_off(); raw_spin_lock_init(&logbuf_lock); return 0; @@ -285,7 +287,7 @@ int printk_bust_lock_safe(void) */ void printk_safe_flush_on_panic(void) { - if (printk_bust_lock_safe() == 0) + if (printk_bust_lock_safe(false) == 0) printk_safe_flush(); } -- 2.16.4
