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authorPetr Mladek <pmladek@suse.com>2022-03-21 14:45:01 +0100
committerPetr Mladek <pmladek@suse.com>2022-03-21 14:45:01 +0100
commit1ccd85f5ac60be460bade24a873800ae6820fbd6 (patch)
tree414ee45b26eb331a292b503e780335598a31e361 /kernel/printk/printk.c
parent0834c6f03b0279d58718f93630206305079645da (diff)
parentce06e863f36f16cdc3b84c7206cd13d5f597d623 (diff)
downloadlinux-1ccd85f5ac60be460bade24a873800ae6820fbd6.tar.bz2
Merge branch 'for-5.18-panic-deadlocks' into for-linus
Diffstat (limited to 'kernel/printk/printk.c')
-rw-r--r--kernel/printk/printk.c55
1 files changed, 54 insertions, 1 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 21fb4e1cd7db..49aa47e876db 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -93,6 +93,12 @@ EXPORT_SYMBOL_GPL(console_drivers);
*/
int __read_mostly suppress_printk;
+/*
+ * During panic, heavy printk by other CPUs can delay the
+ * panic and risk deadlock on console resources.
+ */
+static int __read_mostly suppress_panic_printk;
+
#ifdef CONFIG_LOCKDEP
static struct lockdep_map console_lock_dep_map = {
.name = "console_lock"
@@ -258,6 +264,11 @@ static void __up_console_sem(unsigned long ip)
}
#define up_console_sem() __up_console_sem(_RET_IP_)
+static bool panic_in_progress(void)
+{
+ return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
+}
+
/*
* This is used for debugging the mess that is the VT code by
* keeping track if we have the console semaphore held. It's
@@ -1844,6 +1855,16 @@ static int console_trylock_spinning(void)
if (console_trylock())
return 1;
+ /*
+ * It's unsafe to spin once a panic has begun. If we are the
+ * panic CPU, we may have already halted the owner of the
+ * console_sem. If we are not the panic CPU, then we should
+ * avoid taking console_sem, so the panic CPU has a better
+ * chance of cleanly acquiring it later.
+ */
+ if (panic_in_progress())
+ return 0;
+
printk_safe_enter_irqsave(flags);
raw_spin_lock(&console_owner_lock);
@@ -2219,6 +2240,10 @@ asmlinkage int vprintk_emit(int facility, int level,
if (unlikely(suppress_printk))
return 0;
+ if (unlikely(suppress_panic_printk) &&
+ atomic_read(&panic_cpu) != raw_smp_processor_id())
+ return 0;
+
if (level == LOGLEVEL_SCHED) {
level = LOGLEVEL_DEFAULT;
in_sched = true;
@@ -2587,6 +2612,25 @@ static int have_callable_console(void)
}
/*
+ * Return true when this CPU should unlock console_sem without pushing all
+ * messages to the console. This reduces the chance that the console is
+ * locked when the panic CPU tries to use it.
+ */
+static bool abandon_console_lock_in_panic(void)
+{
+ if (!panic_in_progress())
+ return false;
+
+ /*
+ * We can use raw_smp_processor_id() here because it is impossible for
+ * the task to be migrated to the panic_cpu, or away from it. If
+ * panic_cpu has already been set, and we're not currently executing on
+ * that CPU, then we never will be.
+ */
+ return atomic_read(&panic_cpu) != raw_smp_processor_id();
+}
+
+/*
* Can we actually use the console at this time on this cpu?
*
* Console drivers may assume that per-cpu resources have been allocated. So
@@ -2616,6 +2660,7 @@ void console_unlock(void)
{
static char ext_text[CONSOLE_EXT_LOG_MAX];
static char text[CONSOLE_LOG_MAX];
+ static int panic_console_dropped;
unsigned long flags;
bool do_cond_resched, retry;
struct printk_info info;
@@ -2670,6 +2715,10 @@ skip:
if (console_seq != r.info->seq) {
console_dropped += r.info->seq - console_seq;
console_seq = r.info->seq;
+ if (panic_in_progress() && panic_console_dropped++ > 10) {
+ suppress_panic_printk = 1;
+ pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
+ }
}
if (suppress_message_printing(r.info->level)) {
@@ -2729,6 +2778,10 @@ skip:
if (handover)
return;
+ /* Allow panic_cpu to take over the consoles safely */
+ if (abandon_console_lock_in_panic())
+ break;
+
if (do_cond_resched)
cond_resched();
}
@@ -2746,7 +2799,7 @@ skip:
* flush, no worries.
*/
retry = prb_read_valid(prb, next_seq, NULL);
- if (retry && console_trylock())
+ if (retry && !abandon_console_lock_in_panic() && console_trylock())
goto again;
}
EXPORT_SYMBOL(console_unlock);