From: Petr Mladek <pmladek@suse.com> To: John Ogness <john.ogness@linutronix.de> Cc: Sergey Senozhatsky <senozhatsky@chromium.org>, Steven Rostedt <rostedt@goodmis.org>, "Paul E . McKenney" <paulmck@kernel.org>, frederic@kernel.org, Peter Geis <pgwipeout@gmail.com>, zhouzhouyi@gmail.com, dave@stgolabs.net, josh@joshtriplett.org, Linus Torvalds <torvalds@linux-foundation.org>, rcu@vger.kernel.org, linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com> Subject: [PATCH 1/2] printk: Block console kthreads when direct printing will be required Date: Wed, 15 Jun 2022 18:28:04 +0200 [thread overview] Message-ID: <20220615162805.27962-2-pmladek@suse.com> (raw) In-Reply-To: <20220615162805.27962-1-pmladek@suse.com> 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. BugLink: https://lore.kernel.org/r/20220610205038.GA3050413@paulmck-ThinkPad-P17-Gen-1 BugLink: https://lore.kernel.org/r/CAMdYzYpF4FNTBPZsEFeWRuEwSies36QM_As8osPWZSr2q-viEA@mail.gmail.com Suggested-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Petr Mladek <pmladek@suse.com> --- kernel/printk/printk.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) 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; } -- 2.35.3
WARNING: multiple messages have this Message-ID (diff)
From: Petr Mladek <pmladek@suse.com> To: John Ogness <john.ogness@linutronix.de> Cc: Sergey Senozhatsky <senozhatsky@chromium.org>, Steven Rostedt <rostedt@goodmis.org>, "Paul E . McKenney" <paulmck@kernel.org>, frederic@kernel.org, Peter Geis <pgwipeout@gmail.com>, zhouzhouyi@gmail.com, dave@stgolabs.net, josh@joshtriplett.org, Linus Torvalds <torvalds@linux-foundation.org>, rcu@vger.kernel.org, linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com> Subject: [PATCH 1/2] printk: Block console kthreads when direct printing will be required Date: Wed, 15 Jun 2022 18:28:04 +0200 [thread overview] Message-ID: <20220615162805.27962-2-pmladek@suse.com> (raw) In-Reply-To: <20220615162805.27962-1-pmladek@suse.com> 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. BugLink: https://lore.kernel.org/r/20220610205038.GA3050413@paulmck-ThinkPad-P17-Gen-1 BugLink: https://lore.kernel.org/r/CAMdYzYpF4FNTBPZsEFeWRuEwSies36QM_As8osPWZSr2q-viEA@mail.gmail.com Suggested-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Petr Mladek <pmladek@suse.com> --- kernel/printk/printk.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) 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; } -- 2.35.3 _______________________________________________ Linux-rockchip mailing list Linux-rockchip@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-rockchip
next prev parent reply other threads:[~2022-06-15 16:28 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-06-15 16:28 [PATCH 0/2] printk: Prevent printk kthreads from blocking direct console handling Petr Mladek 2022-06-15 16:28 ` Petr Mladek 2022-06-15 16:28 ` Petr Mladek [this message] 2022-06-15 16:28 ` [PATCH 1/2] printk: Block console kthreads when direct printing will be required Petr Mladek 2022-06-15 17:47 ` Linus Torvalds 2022-06-15 17:47 ` Linus Torvalds 2022-06-15 19:20 ` Petr Mladek 2022-06-15 19:20 ` Petr Mladek 2022-06-15 16:28 ` [PATCH 2/2] printk: Wait for the global console lock when the system is going down Petr Mladek 2022-06-15 16:28 ` Petr Mladek 2022-06-15 17:10 ` [PATCH 0/2] printk: Prevent printk kthreads from blocking direct console handling Paul E. McKenney 2022-06-15 17:10 ` Paul E. McKenney 2022-06-15 20:09 ` Petr Mladek 2022-06-15 20:09 ` Petr Mladek
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20220615162805.27962-2-pmladek@suse.com \ --to=pmladek@suse.com \ --cc=dave@stgolabs.net \ --cc=frederic@kernel.org \ --cc=john.ogness@linutronix.de \ --cc=josh@joshtriplett.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-rockchip@lists.infradead.org \ --cc=paulmck@kernel.org \ --cc=pgwipeout@gmail.com \ --cc=rcu@vger.kernel.org \ --cc=rostedt@goodmis.org \ --cc=senozhatsky@chromium.org \ --cc=torvalds@linux-foundation.org \ --cc=zhouzhouyi@gmail.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.