1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
|
From: Thomas Gleixner <tglx@linutronix.de>
Date: Sat, 16 Sep 2023 21:26:06 +0206
Subject: [PATCH 081/134] printk: nbcon: Add emit function and callback
function for atomic printing
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
Implement an emit function for nbcon consoles to output printk
messages. It utilizes the lockless printk_get_next_message() and
console_prepend_dropped() functions to retrieve/build the output
message. The emit function includes the required safety points to
check for handover/takeover and calls a new write_atomic callback
of the console driver to output the message. It also includes
proper handling for updating the nbcon console sequence number.
A new nbcon_write_context struct is introduced. This is provided
to the write_atomic callback and includes only the information
necessary for performing atomic writes.
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>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230916192007.608398-8-john.ogness@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/console.h | 21 +++++++++
kernel/printk/internal.h | 6 ++
kernel/printk/nbcon.c | 106 ++++++++++++++++++++++++++++++++++++++++++++++-
kernel/printk/printk.c | 9 +--
4 files changed, 134 insertions(+), 8 deletions(-)
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -242,6 +242,7 @@ struct printk_buffers;
* be used only with NBCON_PRIO_PANIC @prio. It
* might cause a system freeze when the console
* is used later.
+ * @backlog: Ringbuffer has pending records
* @pbufs: Pointer to the text buffer for this context
* @seq: The sequence number to print for this context
*/
@@ -252,12 +253,29 @@ struct nbcon_context {
enum nbcon_prio prio;
unsigned int allow_unsafe_takeover : 1;
+ /* members set by emit */
+ unsigned int backlog : 1;
+
/* members set by acquire */
struct printk_buffers *pbufs;
u64 seq;
};
/**
+ * struct nbcon_write_context - Context handed to the nbcon write callbacks
+ * @ctxt: The core console context
+ * @outbuf: Pointer to the text buffer for output
+ * @len: Length to write
+ * @unsafe_takeover: If a hostile takeover in an unsafe state has occurred
+ */
+struct nbcon_write_context {
+ struct nbcon_context __private ctxt;
+ char *outbuf;
+ unsigned int len;
+ bool unsafe_takeover;
+};
+
+/**
* struct console - The console descriptor structure
* @name: The name of the console driver
* @write: Write callback to output messages (Optional)
@@ -277,6 +295,7 @@ struct nbcon_context {
* @data: Driver private data
* @node: hlist node for the console list
*
+ * @write_atomic: Write callback for atomic context
* @nbcon_state: State for nbcon consoles
* @nbcon_seq: Sequence number of the next record for nbcon to print
* @pbufs: Pointer to nbcon private buffer
@@ -301,6 +320,8 @@ struct console {
struct hlist_node node;
/* nbcon console specific members */
+ bool (*write_atomic)(struct console *con,
+ struct nbcon_write_context *wctxt);
atomic_t __private nbcon_state;
atomic_long_t __private nbcon_seq;
struct printk_buffers *pbufs;
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -130,3 +130,9 @@ struct printk_message {
};
bool other_cpu_in_panic(void);
+bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
+ bool is_extended, bool may_supress);
+
+#ifdef CONFIG_PRINTK
+void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped);
+#endif
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -221,7 +221,6 @@ void nbcon_seq_force(struct console *con
* nbcon_seq_force() was used or the current context no longer owns the
* console. In the later case, it will stop printing anyway.
*/
-__maybe_unused
static void nbcon_seq_try_update(struct nbcon_context *ctxt, u64 new_seq)
{
unsigned long nbcon_seq = __seq_to_nbcon_seq(ctxt->seq);
@@ -755,7 +754,6 @@ static bool nbcon_context_can_proceed(st
*
* Internal helper to avoid duplicated code.
*/
-__maybe_unused
static bool __nbcon_context_update_unsafe(struct nbcon_context *ctxt, bool unsafe)
{
struct console *con = ctxt->console;
@@ -785,6 +783,110 @@ static bool __nbcon_context_update_unsaf
}
/**
+ * nbcon_emit_next_record - Emit a record in the acquired context
+ * @wctxt: The write context that will be handed to the write function
+ *
+ * Return: True if this context still owns the console. False if
+ * ownership was handed over or taken.
+ *
+ * When this function returns false then the calling context no longer owns
+ * the console and is no longer allowed to go forward. In this case it must
+ * back out immediately and carefully. The buffer content is also no longer
+ * trusted since it no longer belongs to the calling context. If the caller
+ * wants to do more it must reacquire the console first.
+ *
+ * When true is returned, @wctxt->ctxt.backlog indicates whether there are
+ * still records pending in the ringbuffer,
+ */
+__maybe_unused
+static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt)
+{
+ struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+ struct console *con = ctxt->console;
+ bool is_extended = console_srcu_read_flags(con) & CON_EXTENDED;
+ struct printk_message pmsg = {
+ .pbufs = ctxt->pbufs,
+ };
+ unsigned long con_dropped;
+ struct nbcon_state cur;
+ unsigned long dropped;
+ bool done;
+
+ /*
+ * The printk buffers are filled within an unsafe section. This
+ * prevents NBCON_PRIO_NORMAL and NBCON_PRIO_EMERGENCY from
+ * clobbering each other.
+ */
+
+ if (!nbcon_context_enter_unsafe(ctxt))
+ return false;
+
+ ctxt->backlog = printk_get_next_message(&pmsg, ctxt->seq, is_extended, true);
+ if (!ctxt->backlog)
+ return nbcon_context_exit_unsafe(ctxt);
+
+ /*
+ * @con->dropped is not protected in case of an unsafe hostile
+ * takeover. In that situation the update can be racy so
+ * annotate it accordingly.
+ */
+ con_dropped = data_race(READ_ONCE(con->dropped));
+
+ dropped = con_dropped + pmsg.dropped;
+ if (dropped && !is_extended)
+ console_prepend_dropped(&pmsg, dropped);
+
+ if (!nbcon_context_exit_unsafe(ctxt))
+ return false;
+
+ /* For skipped records just update seq/dropped in @con. */
+ if (pmsg.outbuf_len == 0)
+ goto update_con;
+
+ /* Initialize the write context for driver callbacks. */
+ wctxt->outbuf = &pmsg.pbufs->outbuf[0];
+ wctxt->len = pmsg.outbuf_len;
+ nbcon_state_read(con, &cur);
+ wctxt->unsafe_takeover = cur.unsafe_takeover;
+
+ if (con->write_atomic) {
+ done = con->write_atomic(con, wctxt);
+ } else {
+ nbcon_context_release(ctxt);
+ WARN_ON_ONCE(1);
+ done = false;
+ }
+
+ /* If not done, the emit was aborted. */
+ if (!done)
+ return false;
+
+ /*
+ * Since any dropped message was successfully output, reset the
+ * dropped count for the console.
+ */
+ dropped = 0;
+update_con:
+ /*
+ * The dropped count and the sequence number are updated within an
+ * unsafe section. This limits update races to the panic context and
+ * allows the panic context to win.
+ */
+
+ if (!nbcon_context_enter_unsafe(ctxt))
+ return false;
+
+ if (dropped != con_dropped) {
+ /* Counterpart to the READ_ONCE() above. */
+ WRITE_ONCE(con->dropped, dropped);
+ }
+
+ nbcon_seq_try_update(ctxt, pmsg.seq + 1);
+
+ return nbcon_context_exit_unsafe(ctxt);
+}
+
+/**
* nbcon_alloc - Allocate buffers needed by the nbcon console
* @con: Console to allocate buffers for
*
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -698,9 +698,6 @@ static ssize_t msg_print_ext_body(char *
return len;
}
-static bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
- bool is_extended, bool may_supress);
-
/* /dev/kmsg - userspace message inject/listen interface */
struct devkmsg_user {
atomic64_t seq;
@@ -2733,7 +2730,7 @@ static void __console_unlock(void)
* If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
*/
#ifdef CONFIG_PRINTK
-static void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
+void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
{
struct printk_buffers *pbufs = pmsg->pbufs;
const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
@@ -2787,8 +2784,8 @@ static void console_prepend_dropped(stru
* of @pmsg are valid. (See the documentation of struct printk_message
* for information about the @pmsg fields.)
*/
-static bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
- bool is_extended, bool may_suppress)
+bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
+ bool is_extended, bool may_suppress)
{
static int panic_console_dropped;
|
