When enabled, the dmesg tracefs file enables the redirection of all events to dmesg. This is similar to tp_printk.
Signed-off-by: Vincent Donnefort <[email protected]> diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 2271d54eb3dd..19dfa355b7f3 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -21,6 +21,7 @@ enum tri_type { TRI_CONSUMING, TRI_NONCONSUMING, + TRI_DMESG, }; struct trace_remote_iterator { @@ -43,6 +44,7 @@ struct trace_remote { void *priv; struct trace_buffer *trace_buffer; struct trace_buffer_desc *trace_buffer_desc; + struct trace_remote_iterator *dmesg; struct dentry *dentry; struct eventfs_inode *eventfs_root; struct eventfs_inode *eventfs_subdir; @@ -394,10 +396,15 @@ static int __alloc_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu) return 0; } +static bool trace_remote_do_dmesg(struct trace_remote *remote); + static void trace_remote_do_poll(struct trace_remote *remote) { + bool yield; + ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS); - schedule_delayed_work(&remote->poll_work, msecs_to_jiffies(remote->poll_ms)); + yield = trace_remote_do_dmesg(remote); + schedule_delayed_work(&remote->poll_work, yield ? 0 : msecs_to_jiffies(remote->poll_ms)); } static void __poll_remote(struct work_struct *work) @@ -452,6 +459,14 @@ static struct trace_remote_iterator trace_seq_init(&iter->seq); switch (type) { + case TRI_DMESG: + /* only one printk iter allowed */ + if (WARN_ON_ONCE(remote->dmesg)) { + ret = -EBUSY; + break; + } + smp_store_release(&remote->dmesg, iter); + fallthrough; case TRI_CONSUMING: trace_remote_inc_poll(remote); break; @@ -486,6 +501,11 @@ static void trace_remote_iter_free(struct trace_remote_iterator *iter) lockdep_assert_held(&remote->lock); switch (iter->type) { + case TRI_DMESG: + WARN_ON_ONCE(remote->dmesg != iter); + smp_store_release(&remote->dmesg, NULL); + flush_delayed_work(&remote->poll_work); + fallthrough; case TRI_CONSUMING: trace_remote_dec_poll(remote); break; @@ -498,13 +518,24 @@ static void trace_remote_iter_free(struct trace_remote_iterator *iter) trace_remote_put(remote); } +static bool trace_remote_iter_is_consuming(struct trace_remote_iterator *iter) +{ + switch (iter->type) { + case TRI_CONSUMING: + case TRI_DMESG: + return true; + default: + return false; + } +} + static void trace_remote_iter_read_start(struct trace_remote_iterator *iter) { struct trace_remote *remote = iter->remote; int cpu = iter->cpu; /* Acquire global reader lock */ - if (cpu == RING_BUFFER_ALL_CPUS && iter->type == TRI_CONSUMING) + if (cpu == RING_BUFFER_ALL_CPUS && trace_remote_iter_is_consuming(iter)) down_write(&remote->reader_lock); else down_read(&remote->reader_lock); @@ -521,7 +552,7 @@ static void trace_remote_iter_read_start(struct trace_remote_iterator *iter) if (WARN_ON_ONCE(!remote->pcpu_reader_locks)) return; - if (iter->type == TRI_CONSUMING) + if (trace_remote_iter_is_consuming(iter)) down_write(&remote->pcpu_reader_locks[cpu]); else down_read(&remote->pcpu_reader_locks[cpu]); @@ -538,14 +569,14 @@ static void trace_remote_iter_read_finished(struct trace_remote_iterator *iter) * No need for the remote lock here, iter holds a reference on * remote->nr_readers */ - if (iter->type == TRI_CONSUMING) + if (trace_remote_iter_is_consuming(iter)) up_write(&remote->pcpu_reader_locks[cpu]); else up_read(&remote->pcpu_reader_locks[cpu]); } /* Release global reader lock */ - if (cpu == RING_BUFFER_ALL_CPUS && iter->type == TRI_CONSUMING) + if (cpu == RING_BUFFER_ALL_CPUS && trace_remote_iter_is_consuming(iter)) up_write(&remote->reader_lock); else up_read(&remote->reader_lock); @@ -562,10 +593,9 @@ __peek_event(struct trace_remote_iterator *iter, int cpu, u64 *ts, unsigned long struct ring_buffer_event *rb_evt; struct ring_buffer_iter *rb_iter; - switch (iter->type) { - case TRI_CONSUMING: + if (trace_remote_iter_is_consuming(iter)) { return ring_buffer_peek(iter->remote->trace_buffer, cpu, ts, lost_events); - case TRI_NONCONSUMING: + } else { rb_iter = __get_rb_iter(iter, cpu); if (!rb_iter) return NULL; @@ -629,14 +659,10 @@ static void trace_remote_iter_move(struct trace_remote_iterator *iter) { struct trace_buffer *trace_buffer = iter->remote->trace_buffer; - switch (iter->type) { - case TRI_CONSUMING: + if (trace_remote_iter_is_consuming(iter)) ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL); - break; - case TRI_NONCONSUMING: + else ring_buffer_iter_advance(__get_rb_iter(iter, iter->evt_cpu)); - break; - } } static struct remote_event *trace_remote_find_event(struct trace_remote *remote, unsigned short id); @@ -882,6 +908,86 @@ static const struct file_operations trace_fops = { .release = trace_release, }; +static bool trace_remote_do_dmesg(struct trace_remote *remote) +{ + struct trace_remote_iterator *iter = smp_load_acquire(&remote->dmesg); + unsigned int max_events = 1000; + + if (!iter) + return false; + + trace_remote_iter_read_start(iter); + + while (trace_remote_iter_read_event(iter)) { + trace_seq_init(&iter->seq); + + trace_remote_iter_print_event(iter); + if (!pr_emerg("%s", iter->seq.buffer)) + break; + + trace_remote_iter_move(iter); + + if (!(--max_events)) + break; + } + + trace_remote_iter_read_finished(iter); + + return !max_events; +} + +static int trace_remote_enable_dmesg(struct trace_remote *remote, bool enable) +{ + struct trace_remote_iterator *iter = remote->dmesg; + + lockdep_assert_held(&remote->lock); + + if (enable == !!iter) + return 0; + + if (enable) { + iter = trace_remote_iter(remote, RING_BUFFER_ALL_CPUS, TRI_DMESG); + if (IS_ERR(iter)) + return PTR_ERR(iter); + } else { + trace_remote_iter_free(remote->dmesg); + /* trace_remote_iter_free has reset remote->dmesg */ + } + + return 0; +} + +static ssize_t +dmesg_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos) +{ + struct seq_file *seq = filp->private_data; + struct trace_remote *remote = seq->private; + bool val; + int ret; + + ret = kstrtobool_from_user(ubuf, cnt, &val); + if (ret) + return ret; + + guard(mutex)(&remote->lock); + + ret = trace_remote_enable_dmesg(remote, val); + if (ret) + return ret; + + return cnt; +} + +static int dmesg_show(struct seq_file *s, void *unused) +{ + struct trace_remote *remote = s->private; + + seq_printf(s, "%d\n", !!remote->dmesg); + + return 0; +} +DEFINE_TRACE_REMOTE_ATTRIBUTE(dmesg); + static int trace_remote_init_tracefs(const char *name, struct trace_remote *remote) { struct dentry *remote_d, *percpu_d, *d; @@ -922,6 +1028,10 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo if (!d) goto err; + d = trace_create_file("dmesg", TRACEFS_MODE_WRITE, remote_d, remote, &dmesg_fops); + if (!d) + goto err; + percpu_d = tracefs_create_dir("per_cpu", remote_d); if (!percpu_d) { pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/per_cpu/\n", name); -- 2.54.0.1032.g2f8565e1d1-goog
