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Subject[ANNOUNCE] v5.17-rc1-rt2
Dear RT folks!

I'm pleased to announce the v5.17-rc1-rt2 patch set.

Changes since v5.17-rc1-rt1:

- Update the printk to the latest version. Patch by John Ogness.

Known issues
- netconsole triggers WARN.

- Valentin Schneider reported a few splats on ARM64, see
https://lkml.kernel.org/r/20210810134127.1394269-1-valentin.schneider@arm.com

The delta patch against v5.17-rc1-rt1 is appended below and can be found here:

https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.17/incr/patch-5.17-rc1-rt1-rt2.patch.xz

You can get this release via the git tree at:

git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git v5.17-rc1-rt2

The RT patch against v5.17-rc1 can be found here:

https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.17/older/patch-5.17-rc1-rt2.patch.xz

The split quilt queue is available at:

https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.17/older/patches-5.17-rc1-rt2.tar.xz

Sebastian

diff --git a/kernel/panic.c b/kernel/panic.c
index 0939c67bfb48c..ee7e26d93b410 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -232,6 +232,11 @@ void panic(const char *fmt, ...)
dump_stack();
#endif

+ /* If atomic consoles are available, flush the kernel log. */
+ console_flush_on_panic(CONSOLE_ATOMIC_FLUSH_PENDING);
+
+ bust_spinlocks(1);
+
/*
* If kgdb is enabled, give it a chance to run before we stop all
* the other CPUs or else we won't be able to debug processes left
@@ -239,11 +244,6 @@ void panic(const char *fmt, ...)
*/
kgdb_panic(buf);

- /* Use atomic consoles to dump the kernel log. */
- console_flush_on_panic(CONSOLE_ATOMIC_FLUSH_PENDING);
-
- bust_spinlocks(1);
-
/*
* If we have crashed and we have a crash kernel loaded let it handle
* everything else.
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 6621a4633c2d8..cc04e94c320c4 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2043,8 +2043,10 @@ static u8 *__printk_recursion_counter(void)

int printk_delay_msec __read_mostly;

-static inline void printk_delay(void)
+static inline void printk_delay(int level)
{
+ boot_delay_msec(level);
+
if (unlikely(printk_delay_msec)) {
int m = printk_delay_msec;

@@ -2423,11 +2425,10 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
static void console_lock_spinning_enable(void) { }
static int console_lock_spinning_disable_and_check(void) { return 0; }
static void call_console_driver(struct console *con, const char *text, size_t len,
- char *dropped_text, bool atomic_printing) { }
+ char *dropped_text, bool atomic_printing) {}
static bool suppress_message_printing(int level) { return false; }
-static void start_printk_kthread(struct console *con) { }
-static inline void boot_delay_msec(int level) { }
-static inline void printk_delay(void) { }
+static void printk_delay(int level) {}
+static void start_printk_kthread(struct console *con) {}

#endif /* CONFIG_PRINTK */

@@ -2683,6 +2684,31 @@ int console_trylock(void)
}
EXPORT_SYMBOL(console_trylock);

+/*
+ * A variant of console_trylock() that allows specifying if the context may
+ * sleep. If yes, a trylock on @console_sem is attempted and if successful,
+ * the threaded printers are paused. This is important to ensure that
+ * sleepable contexts do not become involved in console_lock handovers and
+ * will call cond_resched() during the printing loop.
+ */
+static int console_trylock_sched(bool may_schedule)
+{
+ if (!may_schedule)
+ return console_trylock();
+
+ might_sleep();
+
+ if (down_trylock_console_sem())
+ return 0;
+ if (console_suspended) {
+ up_console_sem();
+ return 0;
+ }
+ pause_all_consoles();
+ console_may_schedule = 1;
+ return 1;
+}
+
/*
* This is used to help to make sure that certain paths within the VT code are
* running with the console lock held. It is definitely not the perfect debug
@@ -2836,8 +2862,8 @@ static void write_console_seq(struct console *con, u64 val, bool atomic_printing
*
* @handover will be set to true if a printk waiter has taken over the
* console_lock, in which case the caller is no longer holding the
- * console_lock. A NULL pointer may be provided to disable allowing
- * the console_lock to be taken over by a printk waiter.
+ * console_lock. Otherwise it is set to false. A NULL pointer may be provided
+ * to disable allowing the console_lock to be taken over by a printk waiter.
*/
static bool console_emit_next_record(struct console *con, char *text, char *ext_text,
char *dropped_text, bool atomic_printing,
@@ -2917,8 +2943,7 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_
printk_safe_exit_irqrestore(flags);
}

- boot_delay_msec(r.info->level);
- printk_delay();
+ printk_delay(r.info->level);
skip:
return true;
}
@@ -2935,7 +2960,7 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_
*
* @handover will be set to true if a printk waiter has taken over the
* console_lock, in which case the caller is no longer holding the
- * console_lock.
+ * console_lock. Otherwise it is set to false.
*/
static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
{
@@ -3089,11 +3114,8 @@ void console_unlock(void)
* between lines if allowable. Not doing so can cause a very long
* scheduling stall on a slow console leading to RCU stall and
* softlockup warnings which exacerbate the issue with more
- * messages practically incapacitating the system.
- *
- * console_trylock() is not able to detect the preemptive
- * context reliably. Therefore the value must be stored before
- * and cleared after the "again" goto label.
+ * messages practically incapacitating the system. Therefore, create
+ * a local to use for the printing loop.
*/
do_cond_resched = console_may_schedule;

@@ -3116,7 +3138,7 @@ void console_unlock(void)
* Re-check if there is a new record to flush. If the trylock
* fails, another context is already handling the printing.
*/
- } while (prb_read_valid(prb, next_seq, NULL) && console_trylock());
+ } while (prb_read_valid(prb, next_seq, NULL) && console_trylock_sched(do_cond_resched));
}
EXPORT_SYMBOL(console_unlock);

@@ -3626,6 +3648,7 @@ static int __init printk_late_init(void)
start_printk_kthread(con);
kthreads_started = true;
console_unlock();
+
return 0;
}
late_initcall(printk_late_init);
diff --git a/localversion-rt b/localversion-rt
index 6f206be67cd28..c3054d08a1129 100644
--- a/localversion-rt
+++ b/localversion-rt
@@ -1 +1 @@
--rt1
+-rt2
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