diff options
Diffstat (limited to 'debian/patches-rt/0096-printk-Disable-passing-console-lock-owner-completely.patch')
| -rw-r--r-- | debian/patches-rt/0096-printk-Disable-passing-console-lock-owner-completely.patch | 107 |
1 files changed, 0 insertions, 107 deletions
diff --git a/debian/patches-rt/0096-printk-Disable-passing-console-lock-owner-completely.patch b/debian/patches-rt/0096-printk-Disable-passing-console-lock-owner-completely.patch deleted file mode 100644 index d5dcdcdcc..000000000 --- a/debian/patches-rt/0096-printk-Disable-passing-console-lock-owner-completely.patch +++ /dev/null @@ -1,107 +0,0 @@ -From: Petr Mladek <pmladek@suse.com> -Date: Fri, 13 Oct 2023 14:12:05 +0000 -Subject: [PATCH 096/134] printk: Disable passing console lock owner completely - during panic() -Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz - -The commit d51507098ff91 ("printk: disable optimistic spin -during panic") added checks to avoid becoming a console waiter -if a panic is in progress. - -However, the transition to panic can occur while there is -already a waiter. The current owner should not pass the lock to -the waiter because it might get stopped or blocked anytime. - -Also the panic context might pass the console lock owner to an -already stopped waiter by mistake. It might happen when -console_flush_on_panic() ignores the current lock owner, for -example: - -CPU0 CPU1 ----- ---- -console_lock_spinning_enable() - console_trylock_spinning() - [CPU1 now console waiter] -NMI: panic() - panic_other_cpus_shutdown() - [stopped as console waiter] - console_flush_on_panic() - console_lock_spinning_enable() - [print 1 record] - console_lock_spinning_disable_and_check() - [handover to stopped CPU1] - -This results in panic() not flushing the panic messages. - -Fix these problems by disabling all spinning operations -completely during panic(). - -Another advantage is that it prevents possible deadlocks caused -by "console_owner_lock". The panic() context does not need to -take it any longer. The lockless checks are safe because the -functions become NOPs when they see the panic in progress. All -operations manipulating the state are still synchronized by the -lock even when non-panic CPUs would notice the panic -synchronously. - -The current owner might stay spinning. But non-panic() CPUs -would get stopped anyway and the panic context will never start -spinning. - -Fixes: dbdda842fe96 ("printk: Add console owner and waiter logic to load balance console writes") -Signed-off-by: Petr Mladek <pmladek@suse.com> -Signed-off-by: John Ogness <john.ogness@linutronix.de> -Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> ---- - kernel/printk/printk.c | 29 +++++++++++++++++++++++++++++ - 1 file changed, 29 insertions(+) - ---- a/kernel/printk/printk.c -+++ b/kernel/printk/printk.c -@@ -1870,10 +1870,23 @@ static bool console_waiter; - */ - static void console_lock_spinning_enable(void) - { -+ /* -+ * Do not use spinning in panic(). The panic CPU wants to keep the lock. -+ * Non-panic CPUs abandon the flush anyway. -+ * -+ * Just keep the lockdep annotation. The panic-CPU should avoid -+ * taking console_owner_lock because it might cause a deadlock. -+ * This looks like the easiest way how to prevent false lockdep -+ * reports without handling races a lockless way. -+ */ -+ if (panic_in_progress()) -+ goto lockdep; -+ - raw_spin_lock(&console_owner_lock); - console_owner = current; - raw_spin_unlock(&console_owner_lock); - -+lockdep: - /* The waiter may spin on us after setting console_owner */ - spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); - } -@@ -1898,6 +1911,22 @@ static int console_lock_spinning_disable - { - int waiter; - -+ /* -+ * Ignore spinning waiters during panic() because they might get stopped -+ * or blocked at any time, -+ * -+ * It is safe because nobody is allowed to start spinning during panic -+ * in the first place. If there has been a waiter then non panic CPUs -+ * might stay spinning. They would get stopped anyway. The panic context -+ * will never start spinning and an interrupted spin on panic CPU will -+ * never continue. -+ */ -+ if (panic_in_progress()) { -+ /* Keep lockdep happy. */ -+ spin_release(&console_owner_dep_map, _THIS_IP_); -+ return 0; -+ } -+ - raw_spin_lock(&console_owner_lock); - waiter = READ_ONCE(console_waiter); - console_owner = NULL; |