Messages in this thread Patch in this message | | | From | John Ogness <> | Subject | [PATCH printk v2 04/11] printk: nbcon: Provide functions to mark atomic write sections | Date | Wed, 20 Sep 2023 01:14:49 +0206 |
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From: Thomas Gleixner <tglx@linutronix.de>
WARN/OOPS/PANIC require printing out immediately since the regular printing method (and in the future, the printing threads) might not be able to run.
Add per-CPU state to denote the priority/urgency of the output and provide functions to mark the beginning and end of sections where the urgent messages are generated.
Note that when a CPU is in a priority elevated state, flushing only occurs when dropping back to a lower priority. This allows the full set of printk records (WARN/OOPS/PANIC output) to be stored in the ringbuffer before beginning to flush the backlog.
Co-developed-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de> --- include/linux/console.h | 4 ++ kernel/printk/nbcon.c | 89 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 93 insertions(+)
diff --git a/include/linux/console.h b/include/linux/console.h index e4fc6f7c1496..25a3ddd39083 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -452,10 +452,14 @@ static inline bool console_is_registered(const struct console *con) hlist_for_each_entry(con, &console_list, node) #ifdef CONFIG_PRINTK +extern enum nbcon_prio nbcon_atomic_enter(enum nbcon_prio prio); +extern void nbcon_atomic_exit(enum nbcon_prio prio, enum nbcon_prio prev_prio); extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt); extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt); extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt); #else +static inline enum nbcon_prio nbcon_atomic_enter(enum nbcon_prio prio) { return NBCON_PRIO_NONE; } +static inline void nbcon_atomic_exit(enum nbcon_prio prio, enum nbcon_prio prev_prio) { } static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; } static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; } static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; } diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index b96077152f49..9359906b575b 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -961,6 +961,95 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt) return nbcon_context_exit_unsafe(ctxt); } +/** + * struct nbcon_cpu_state - Per CPU printk context state + * @prio: The current context priority level + * @nesting: Per priority nest counter + */ +struct nbcon_cpu_state { + enum nbcon_prio prio; + int nesting[NBCON_PRIO_MAX]; +}; + +static DEFINE_PER_CPU(struct nbcon_cpu_state, nbcon_pcpu_state); +static struct nbcon_cpu_state early_nbcon_pcpu_state __initdata; + +/** + * nbcon_get_cpu_state - Get the per CPU console state pointer + * + * Returns either a pointer to the per CPU state of the current CPU or to + * the init data state during early boot. + */ +static __ref struct nbcon_cpu_state *nbcon_get_cpu_state(void) +{ + if (!printk_percpu_data_ready()) + return &early_nbcon_pcpu_state; + + return this_cpu_ptr(&nbcon_pcpu_state); +} + +/** + * nbcon_atomic_enter - Enter a context that enforces atomic printing + * @prio: Priority of the context + * + * Return: The previous priority that needs to be fed into + * the corresponding nbcon_atomic_exit() + * Context: Any context. Disables migration. + */ +enum nbcon_prio nbcon_atomic_enter(enum nbcon_prio prio) +{ + struct nbcon_cpu_state *cpu_state; + enum nbcon_prio prev_prio; + + migrate_disable(); + + cpu_state = nbcon_get_cpu_state(); + + prev_prio = cpu_state->prio; + if (prio > prev_prio) + cpu_state->prio = prio; + + /* + * Increment the nesting on @cpu_state->prio (instead of + * @prio) so that a WARN() nested within a panic printout + * does not attempt to scribble state. + */ + cpu_state->nesting[cpu_state->prio]++; + + return prev_prio; +} + +/** + * nbcon_atomic_exit - Exit a context that enforces atomic printing + * @prio: Priority of the context to leave + * @prev_prio: Priority of the previous context for restore + * + * Context: Any context. Enables migration. + * + * @prev_prio is the priority returned by the corresponding + * nbcon_atomic_enter(). + */ +void nbcon_atomic_exit(enum nbcon_prio prio, enum nbcon_prio prev_prio) +{ + struct nbcon_cpu_state *cpu_state; + + cpu_state = nbcon_get_cpu_state(); + + /* + * Undo the nesting of nbcon_atomic_enter() at the CPU state + * priority. + */ + cpu_state->nesting[cpu_state->prio]--; + + /* + * Restore the previous priority, which was returned by + * nbcon_atomic_enter(). + */ + cpu_state->prio = prev_prio; + + migrate_enable(); +} + /** * nbcon_alloc - Allocate buffers needed by the nbcon console * @con: Console to allocate buffers for -- 2.39.2
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