When enabled, the printk 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 21583fae1bd9..1bf0ba159c92 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_PRINTK, }; struct trace_remote_iterator { @@ -42,6 +43,7 @@ struct trace_remote { void *priv; struct trace_buffer *trace_buffer; struct trace_buffer_desc *trace_buffer_desc; + struct trace_remote_iterator *printk; struct dentry *dentry; struct eventfs_inode *eventfs_root; struct eventfs_inode *eventfs_subdir; @@ -335,6 +337,8 @@ static int __alloc_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu) return 0; } +static void trace_remote_do_printk(struct trace_remote *remote); + static void __poll_remote(struct work_struct *work) { struct delayed_work *dwork = to_delayed_work(work); @@ -342,6 +346,7 @@ static void __poll_remote(struct work_struct *work) remote = container_of(dwork, struct trace_remote, poll_work); ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS); + trace_remote_do_printk(remote); schedule_delayed_work(dwork, msecs_to_jiffies(remote->poll_ms)); } @@ -351,6 +356,8 @@ static void trace_remote_inc_poll(struct trace_remote *remote) /* poll_cnt <= nr_readers, inherits its overflow protection */ if (!remote->poll_cnt++) { ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS); + trace_remote_do_printk(remote); + schedule_delayed_work(&remote->poll_work, msecs_to_jiffies(remote->poll_ms)); } } @@ -393,6 +400,14 @@ static struct trace_remote_iterator trace_seq_init(&iter->seq); switch (type) { + case TRI_PRINTK: + /* only one printk iter allowed */ + if (WARN_ON_ONCE(remote->printk)) { + ret = -EBUSY; + break; + } + smp_store_release(&remote->printk, iter); + fallthrough; case TRI_CONSUMING: trace_remote_inc_poll(remote); break; @@ -427,6 +442,11 @@ static void trace_remote_iter_free(struct trace_remote_iterator *iter) lockdep_assert_held(&remote->lock); switch (iter->type) { + case TRI_PRINTK: + WARN_ON_ONCE(remote->printk != iter); + smp_store_release(&remote->printk, NULL); + flush_delayed_work(&remote->poll_work); + fallthrough; case TRI_CONSUMING: trace_remote_dec_poll(remote); break; @@ -504,6 +524,7 @@ __peek_event(struct trace_remote_iterator *iter, int cpu, u64 *ts, unsigned long struct ring_buffer_iter *rb_iter; switch (iter->type) { + case TRI_PRINTK: case TRI_CONSUMING: return ring_buffer_peek(iter->remote->trace_buffer, cpu, ts, lost_events); case TRI_NONCONSUMING: @@ -571,6 +592,7 @@ 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_PRINTK: case TRI_CONSUMING: ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL); break; @@ -814,6 +836,80 @@ static const struct file_operations trace_fops = { .release = trace_release, }; +static void trace_remote_do_printk(struct trace_remote *remote) +{ + struct trace_remote_iterator *iter = smp_load_acquire(&remote->printk); + + if (!iter) + return; + + 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); + } + + trace_remote_iter_read_finished(iter); +} + +static int trace_remote_enable_printk(struct trace_remote *remote, bool enable) +{ + struct trace_remote_iterator *iter = remote->printk; + + lockdep_assert_held(&remote->lock); + + if (enable == !!iter) + return 0; + + if (enable) { + iter = trace_remote_iter(remote, RING_BUFFER_ALL_CPUS, TRI_PRINTK); + if (IS_ERR(iter)) + return PTR_ERR(iter); + } else { + trace_remote_iter_free(remote->printk); + /* trace_remote_iter_free has reset remote->printk */ + } + + return 0; +} + +static ssize_t +printk_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_printk(remote, val); + if (ret) + return ret; + + return cnt; +} + +static int printk_show(struct seq_file *s, void *unused) +{ + struct trace_remote *remote = s->private; + + seq_printf(s, "%d\n", !!remote->printk); + + return 0; +} +DEFINE_SHOW_STORE_ATTRIBUTE(printk); + static struct dentry *tracefs_root; static DEFINE_MUTEX(tracefs_lock); static u64 tracefs_root_count; @@ -858,6 +954,10 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo if (!d) goto err; + d = trace_create_file("printk", TRACEFS_MODE_WRITE, remote_d, remote, &printk_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
