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authorPetr Mladek <pmladek@suse.com>2022-06-15 18:28:04 +0200
committerPetr Mladek <pmladek@suse.com>2022-06-15 22:03:38 +0200
commitc3230283e2819a69dad2cf7a63143fde8bab8b5c (patch)
tree3c805018c62d4e31aa50fbe1dd0572656aec300e /kernel
parent809631e2bff5aba056df75cc4e43127dbd0278c9 (diff)
printk: Block console kthreads when direct printing will be required
There are known situations when the console kthreads are not reliable or does not work in principle, for example, early boot, panic, shutdown. For these situations there is the direct (legacy) mode when printk() tries to get console_lock() and flush the messages directly. It works very well during the early boot when the console kthreads are not available at all. It gets more complicated in the other situations when console kthreads might be actively printing and block console_trylock() in printk(). The same problem is in the legacy code as well. Any console_lock() owner could block console_trylock() in printk(). It is solved by a trick that the current console_lock() owner is responsible for printing all pending messages. It is actually the reason why there is the risk of softlockups and why the console kthreads were introduced. The console kthreads use the same approach. They are responsible for printing the messages by definition. So that they handle the messages anytime when they are awake and see new ones. The global console_lock is available when there is nothing to do. It should work well when the problematic context is correctly detected and printk() switches to the direct mode. But it seems that it is not enough in practice. There are reports that the messages are not printed during panic() or shutdown() even though printk() tries to use the direct mode here. The problem seems to be that console kthreads become active in these situation as well. They steel the job before other CPUs are stopped. Then they are stopped in the middle of the job and block the global console_lock. First part of the solution is to block console kthreads when the system is in a problematic state and requires the direct printk() mode. Link: https://lore.kernel.org/r/20220610205038.GA3050413@paulmck-ThinkPad-P17-Gen-1 Link: https://lore.kernel.org/r/CAMdYzYpF4FNTBPZsEFeWRuEwSies36QM_As8osPWZSr2q-viEA@mail.gmail.com Suggested-by: John Ogness <john.ogness@linutronix.de> Tested-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20220615162805.27962-2-pmladek@suse.com
Diffstat (limited to 'kernel')
-rw-r--r--kernel/printk/printk.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ea3dd55709e7..45c6c2b0b104 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3729,7 +3729,9 @@ static bool printer_should_wake(struct console *con, u64 seq)
return true;
if (con->blocked ||
- console_kthreads_atomically_blocked()) {
+ console_kthreads_atomically_blocked() ||
+ system_state > SYSTEM_RUNNING ||
+ oops_in_progress) {
return false;
}