Allow a magic sysrq to be triggered from an NMI context. This is done via marking some sysrq actions as NMI safe. Safe actions will be allowed to run from NMI context whilst that cannot run from an NMI will be queued as irq_work for later processing. A particular sysrq handler is only marked as NMI safe in case the handler isn't contending for any synchronization primitives as in NMI context they are expected to cause deadlocks. Note that the debug sysrq do not contend for any synchronization primitives. It does call kgdb_breakpoint() to provoke a trap but that trap handler should be NMI safe on architectures that implement an NMI. Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx> --- Hi Hitomi Hasegawa, Give this patch a try with diagnostic pseudo NMI interrupt on A64FX and let me know if it works for you. Also, feel free to include this patch along with your driver patch. -Sumit Changes in v2: - Rebased to 5.17-rc5. - Separate this patch from complete patch-set [1] as its relevant for other diagnostic NMI interrupts [2] as well apart from uart NMI interrupts. - Incorporated suggestions from Doug. [1] https://lore.kernel.org/linux-arm-kernel/CAFA6WYOWHgmYYt=KGXDh2hKiuy_rQbJfi279ev0+s-Qh7L21kA@xxxxxxxxxxxxxx/t/#m2b5006f08581448020eb24566927a104d0b95c44 [2] https://lore.kernel.org/all/Yhi0rrkSR63ZhjX1@xxxxxxxxx/T/ drivers/tty/sysrq.c | 51 ++++++++++++++++++++++++++++++++++++++- include/linux/sysrq.h | 1 + kernel/debug/debug_core.c | 1 + 3 files changed, 52 insertions(+), 1 deletion(-) diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index bbfd004449b5..0ce944591036 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -51,6 +51,8 @@ #include <linux/syscalls.h> #include <linux/of.h> #include <linux/rcupdate.h> +#include <linux/irq_work.h> +#include <linux/kfifo.h> #include <asm/ptrace.h> #include <asm/irq_regs.h> @@ -112,6 +114,7 @@ static const struct sysrq_key_op sysrq_loglevel_op = { .help_msg = "loglevel(0-9)", .action_msg = "Changing Loglevel", .enable_mask = SYSRQ_ENABLE_LOG, + .nmi_safe = true, }; #ifdef CONFIG_VT @@ -159,6 +162,7 @@ static const struct sysrq_key_op sysrq_crash_op = { .help_msg = "crash(c)", .action_msg = "Trigger a crash", .enable_mask = SYSRQ_ENABLE_DUMP, + .nmi_safe = true, }; static void sysrq_handle_reboot(int key) @@ -172,6 +176,7 @@ static const struct sysrq_key_op sysrq_reboot_op = { .help_msg = "reboot(b)", .action_msg = "Resetting", .enable_mask = SYSRQ_ENABLE_BOOT, + .nmi_safe = true, }; const struct sysrq_key_op *__sysrq_reboot_op = &sysrq_reboot_op; @@ -219,6 +224,7 @@ static const struct sysrq_key_op sysrq_showlocks_op = { .handler = sysrq_handle_showlocks, .help_msg = "show-all-locks(d)", .action_msg = "Show Locks Held", + .nmi_safe = true, }; #else #define sysrq_showlocks_op (*(const struct sysrq_key_op *)NULL) @@ -291,6 +297,7 @@ static const struct sysrq_key_op sysrq_showregs_op = { .help_msg = "show-registers(p)", .action_msg = "Show Regs", .enable_mask = SYSRQ_ENABLE_DUMP, + .nmi_safe = true, }; static void sysrq_handle_showstate(int key) @@ -328,6 +335,7 @@ static const struct sysrq_key_op sysrq_ftrace_dump_op = { .help_msg = "dump-ftrace-buffer(z)", .action_msg = "Dump ftrace buffer", .enable_mask = SYSRQ_ENABLE_DUMP, + .nmi_safe = true, }; #else #define sysrq_ftrace_dump_op (*(const struct sysrq_key_op *)NULL) @@ -566,6 +574,37 @@ static void __sysrq_put_key_op(int key, const struct sysrq_key_op *op_p) sysrq_key_table[i] = op_p; } +#define SYSRQ_NMI_FIFO_SIZE 2 +static DEFINE_KFIFO(sysrq_nmi_fifo, int, SYSRQ_NMI_FIFO_SIZE); + +static void sysrq_do_nmi_work(struct irq_work *work) +{ + const struct sysrq_key_op *op_p; + int orig_suppress_printk; + int key; + + orig_suppress_printk = suppress_printk; + suppress_printk = 0; + + rcu_sysrq_start(); + rcu_read_lock(); + + if (kfifo_peek(&sysrq_nmi_fifo, &key)) { + op_p = __sysrq_get_key_op(key); + if (op_p) + op_p->handler(key); + } + + rcu_read_unlock(); + rcu_sysrq_end(); + + suppress_printk = orig_suppress_printk; + + kfifo_reset_out(&sysrq_nmi_fifo); +} + +static DEFINE_IRQ_WORK(sysrq_nmi_work, sysrq_do_nmi_work); + void __handle_sysrq(int key, bool check_mask) { const struct sysrq_key_op *op_p; @@ -573,6 +612,10 @@ void __handle_sysrq(int key, bool check_mask) int orig_suppress_printk; int i; + /* Skip sysrq handling if one already in progress */ + if (!kfifo_is_empty(&sysrq_nmi_fifo)) + return; + orig_suppress_printk = suppress_printk; suppress_printk = 0; @@ -596,7 +639,13 @@ void __handle_sysrq(int key, bool check_mask) if (!check_mask || sysrq_on_mask(op_p->enable_mask)) { pr_info("%s\n", op_p->action_msg); console_loglevel = orig_log_level; - op_p->handler(key); + + if (in_nmi() && !op_p->nmi_safe) { + kfifo_put(&sysrq_nmi_fifo, key); + irq_work_queue(&sysrq_nmi_work); + } else { + op_p->handler(key); + } } else { pr_info("This sysrq operation is disabled.\n"); console_loglevel = orig_log_level; diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h index 3a582ec7a2f1..630b5b9dc225 100644 --- a/include/linux/sysrq.h +++ b/include/linux/sysrq.h @@ -34,6 +34,7 @@ struct sysrq_key_op { const char * const help_msg; const char * const action_msg; const int enable_mask; + const bool nmi_safe; }; #ifdef CONFIG_MAGIC_SYSRQ diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c index da06a5553835..53b56114f59b 100644 --- a/kernel/debug/debug_core.c +++ b/kernel/debug/debug_core.c @@ -978,6 +978,7 @@ static const struct sysrq_key_op sysrq_dbg_op = { .handler = sysrq_handle_dbg, .help_msg = "debug(g)", .action_msg = "DEBUG", + .nmi_safe = true, }; #endif -- 2.25.1
