diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/printk/internal.h | 2 | ||||
| -rw-r--r-- | kernel/printk/nbcon.c | 89 | ||||
| -rw-r--r-- | kernel/printk/printk.c | 20 |
3 files changed, 78 insertions, 33 deletions
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index bbed41ad29cf..ef282001f200 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -64,6 +64,7 @@ struct dev_printk_info; extern struct printk_ringbuffer *prb; extern bool printk_kthreads_running; +extern bool printk_kthreads_ready; extern bool debug_non_panic_cpus; __printf(4, 0) @@ -179,6 +180,7 @@ static inline void nbcon_kthread_wake(struct console *con) #define PRINTKRB_RECORD_MAX 0 #define printk_kthreads_running (false) +#define printk_kthreads_ready (false) /* * In !PRINTK builds we still export console_sem diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index fd12efcc4aed..646801813415 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -214,8 +214,9 @@ static void nbcon_seq_try_update(struct nbcon_context *ctxt, u64 new_seq) /** * nbcon_context_try_acquire_direct - Try to acquire directly - * @ctxt: The context of the caller - * @cur: The current console state + * @ctxt: The context of the caller + * @cur: The current console state + * @is_reacquire: This acquire is a reacquire * * Acquire the console when it is released. Also acquire the console when * the current owner has a lower priority and the console is in a safe state. @@ -225,17 +226,17 @@ static void nbcon_seq_try_update(struct nbcon_context *ctxt, u64 new_seq) * * Errors: * - * -EPERM: A panic is in progress and this is not the panic CPU. - * Or the current owner or waiter has the same or higher - * priority. No acquire method can be successful in - * this case. + * -EPERM: A panic is in progress and this is neither the panic + * CPU nor is this a reacquire. Or the current owner or + * waiter has the same or higher priority. No acquire + * method can be successful in these cases. * * -EBUSY: The current owner has a lower priority but the console * in an unsafe state. The caller should try using * the handover acquire method. */ static int nbcon_context_try_acquire_direct(struct nbcon_context *ctxt, - struct nbcon_state *cur) + struct nbcon_state *cur, bool is_reacquire) { unsigned int cpu = smp_processor_id(); struct console *con = ctxt->console; @@ -243,14 +244,20 @@ static int nbcon_context_try_acquire_direct(struct nbcon_context *ctxt, do { /* - * Panic does not imply that the console is owned. However, it - * is critical that non-panic CPUs during panic are unable to - * acquire ownership in order to satisfy the assumptions of - * nbcon_waiter_matches(). In particular, the assumption that - * lower priorities are ignored during panic. + * Panic does not imply that the console is owned. However, + * since all non-panic CPUs are stopped during panic(), it + * is safer to have them avoid gaining console ownership. + * + * If this acquire is a reacquire (and an unsafe takeover + * has not previously occurred) then it is allowed to attempt + * a direct acquire in panic. This gives console drivers an + * opportunity to perform any necessary cleanup if they were + * interrupted by the panic CPU while printing. */ - if (other_cpu_in_panic()) + if (other_cpu_in_panic() && + (!is_reacquire || cur->unsafe_takeover)) { return -EPERM; + } if (ctxt->prio <= cur->prio || ctxt->prio <= cur->req_prio) return -EPERM; @@ -301,8 +308,9 @@ static bool nbcon_waiter_matches(struct nbcon_state *cur, int expected_prio) * Event #1 implies this context is EMERGENCY. * Event #2 implies the new context is PANIC. * Event #3 occurs when panic() has flushed the console. - * Events #4 and #5 are not possible due to the other_cpu_in_panic() - * check in nbcon_context_try_acquire_direct(). + * Event #4 occurs when a non-panic CPU reacquires. + * Event #5 is not possible due to the other_cpu_in_panic() check + * in nbcon_context_try_acquire_handover(). */ return (cur->req_prio == expected_prio); @@ -431,6 +439,16 @@ static int nbcon_context_try_acquire_handover(struct nbcon_context *ctxt, WARN_ON_ONCE(ctxt->prio <= cur->prio || ctxt->prio <= cur->req_prio); WARN_ON_ONCE(!cur->unsafe); + /* + * Panic does not imply that the console is owned. However, it + * is critical that non-panic CPUs during panic are unable to + * wait for a handover in order to satisfy the assumptions of + * nbcon_waiter_matches(). In particular, the assumption that + * lower priorities are ignored during panic. + */ + if (other_cpu_in_panic()) + return -EPERM; + /* Handover is not possible on the same CPU. */ if (cur->cpu == cpu) return -EBUSY; @@ -558,7 +576,8 @@ static struct printk_buffers panic_nbcon_pbufs; /** * nbcon_context_try_acquire - Try to acquire nbcon console - * @ctxt: The context of the caller + * @ctxt: The context of the caller + * @is_reacquire: This acquire is a reacquire * * Context: Under @ctxt->con->device_lock() or local_irq_save(). * Return: True if the console was acquired. False otherwise. @@ -568,7 +587,7 @@ static struct printk_buffers panic_nbcon_pbufs; * in an unsafe state. Otherwise, on success the caller may assume * the console is not in an unsafe state. */ -static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) +static bool nbcon_context_try_acquire(struct nbcon_context *ctxt, bool is_reacquire) { unsigned int cpu = smp_processor_id(); struct console *con = ctxt->console; @@ -577,7 +596,7 @@ static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) nbcon_state_read(con, &cur); try_again: - err = nbcon_context_try_acquire_direct(ctxt, &cur); + err = nbcon_context_try_acquire_direct(ctxt, &cur, is_reacquire); if (err != -EBUSY) goto out; @@ -913,7 +932,7 @@ void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) { struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); - while (!nbcon_context_try_acquire(ctxt)) + while (!nbcon_context_try_acquire(ctxt, true)) cpu_relax(); nbcon_write_context_set_buf(wctxt, NULL, 0); @@ -1101,7 +1120,7 @@ static bool nbcon_emit_one(struct nbcon_write_context *wctxt, bool use_atomic) cant_migrate(); } - if (!nbcon_context_try_acquire(ctxt)) + if (!nbcon_context_try_acquire(ctxt, false)) goto out; /* @@ -1486,7 +1505,7 @@ static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq, ctxt->prio = nbcon_get_default_prio(); ctxt->allow_unsafe_takeover = allow_unsafe_takeover; - if (!nbcon_context_try_acquire(ctxt)) + if (!nbcon_context_try_acquire(ctxt, false)) return -EPERM; while (nbcon_seq_read(con) < stop_seq) { @@ -1671,6 +1690,9 @@ bool nbcon_alloc(struct console *con) { struct nbcon_state state = { }; + /* Synchronize the kthread start. */ + lockdep_assert_console_list_lock_held(); + /* The write_thread() callback is mandatory. */ if (WARN_ON(!con->write_thread)) return false; @@ -1701,12 +1723,15 @@ bool nbcon_alloc(struct console *con) return false; } - if (printk_kthreads_running) { + if (printk_kthreads_ready && !have_boot_console) { if (!nbcon_kthread_create(con)) { kfree(con->pbufs); con->pbufs = NULL; return false; } + + /* Might be the first kthread. */ + printk_kthreads_running = true; } } @@ -1716,14 +1741,30 @@ bool nbcon_alloc(struct console *con) /** * nbcon_free - Free and cleanup the nbcon console specific data * @con: Console to free/cleanup nbcon data + * + * Important: @have_nbcon_console must be updated before calling + * this function. In particular, it can be set only when there + * is still another nbcon console registered. */ void nbcon_free(struct console *con) { struct nbcon_state state = { }; - if (printk_kthreads_running) + /* Synchronize the kthread stop. */ + lockdep_assert_console_list_lock_held(); + + if (printk_kthreads_running) { nbcon_kthread_stop(con); + /* Might be the last nbcon console. + * + * Do not rely on printk_kthreads_check_locked(). It is not + * called in some code paths, see nbcon_free() callers. + */ + if (!have_nbcon_console) + printk_kthreads_running = false; + } + nbcon_state_set(con, &state); /* Boot consoles share global printk buffers. */ @@ -1762,7 +1803,7 @@ bool nbcon_device_try_acquire(struct console *con) ctxt->console = con; ctxt->prio = NBCON_PRIO_NORMAL; - if (!nbcon_context_try_acquire(ctxt)) + if (!nbcon_context_try_acquire(ctxt, false)) return false; if (!nbcon_context_enter_unsafe(ctxt)) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 1eea80d0648e..0efbcdda9aab 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3574,7 +3574,7 @@ EXPORT_SYMBOL(console_resume); static int unregister_console_locked(struct console *console); /* True when system boot is far enough to create printer threads. */ -static bool printk_kthreads_ready __ro_after_init; +bool printk_kthreads_ready __ro_after_init; static struct task_struct *printk_legacy_kthread; @@ -3713,6 +3713,7 @@ static void printk_kthreads_check_locked(void) if (!printk_kthreads_ready) return; + /* Start or stop the legacy kthread when needed. */ if (have_legacy_console || have_boot_console) { if (!printk_legacy_kthread && force_legacy_kthread() && @@ -4204,14 +4205,6 @@ static int unregister_console_locked(struct console *console) */ synchronize_srcu(&console_srcu); - if (console->flags & CON_NBCON) - nbcon_free(console); - - console_sysfs_notify(); - - if (console->exit) - res = console->exit(console); - /* * With this console gone, the global flags tracking registered * console types may have changed. Update them. @@ -4232,6 +4225,15 @@ static int unregister_console_locked(struct console *console) if (!found_nbcon_con) have_nbcon_console = found_nbcon_con; + /* @have_nbcon_console must be updated before calling nbcon_free(). */ + if (console->flags & CON_NBCON) + nbcon_free(console); + + console_sysfs_notify(); + + if (console->exit) + res = console->exit(console); + /* Changed console list, may require printer threads to start/stop. */ printk_kthreads_check_locked(); |