100 lines
3.9 KiB
Diff
100 lines
3.9 KiB
Diff
From c6361018e388b05431e3f03c465861ca58f49e4b Mon Sep 17 00:00:00 2001
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From: John Ogness <john.ogness@linutronix.de>
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Date: Fri, 20 Oct 2023 10:01:58 +0000
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Subject: [PATCH 155/196] printk: nbcon: Provide function to reacquire
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ownership
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Contexts may become nbcon owners for various reasons, not just
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for printing. Indeed, the port->lock wrapper takes ownership
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for anything relating to the hardware.
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Since ownership can be lost at any time due to handover or
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takeover, a context _should_ be prepared to back out
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immediately and carefully. However, there are many scenarios
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where the context _must_ reacquire ownership in order to
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finalize or revert hardware changes.
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One such example is when interrupts are disabled by a context.
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No other context will automagically re-enable the interrupts.
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For this case, the disabling context _must_ reacquire nbcon
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ownership so that it can re-enable the interrupts.
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Provide nbcon_reacquire() for exactly this purpose.
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Note that for printing contexts, after a successful reacquire
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the context will have no output buffer because that has been
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lost. nbcon_reacquire() cannot be used to resume printing.
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Signed-off-by: John Ogness <john.ogness@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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include/linux/console.h | 2 ++
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kernel/printk/nbcon.c | 32 ++++++++++++++++++++++++++++++++
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2 files changed, 34 insertions(+)
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diff --git a/include/linux/console.h b/include/linux/console.h
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index 982c98280ae8..f8a062867888 100644
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--- a/include/linux/console.h
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+++ b/include/linux/console.h
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@@ -474,12 +474,14 @@ extern void nbcon_cpu_emergency_exit(void);
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extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt);
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extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt);
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extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt);
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+extern void nbcon_reacquire(struct nbcon_write_context *wctxt);
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#else
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static inline void nbcon_cpu_emergency_enter(void) { }
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static inline void nbcon_cpu_emergency_exit(void) { }
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static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; }
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static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; }
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static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; }
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+static inline void nbcon_reacquire(struct nbcon_write_context *wctxt) { }
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#endif
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extern int console_set_on_cmdline;
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diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
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index b866d0138fe0..f843df54ee82 100644
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--- a/kernel/printk/nbcon.c
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+++ b/kernel/printk/nbcon.c
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@@ -830,6 +830,38 @@ bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt)
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}
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EXPORT_SYMBOL_GPL(nbcon_exit_unsafe);
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+/**
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+ * nbcon_reacquire - Reacquire a console after losing ownership
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+ * @wctxt: The write context that was handed to the write function
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+ *
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+ * Since ownership can be lost at any time due to handover or takeover, a
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+ * printing context _should_ be prepared to back out immediately and
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+ * carefully. However, there are many scenarios where the context _must_
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+ * reacquire ownership in order to finalize or revert hardware changes.
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+ *
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+ * This function allows a context to reacquire ownership using the same
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+ * priority as its previous ownership.
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+ *
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+ * Note that for printing contexts, after a successful reacquire the
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+ * context will have no output buffer because that has been lost. This
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+ * function cannot be used to resume printing.
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+ */
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+void nbcon_reacquire(struct nbcon_write_context *wctxt)
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+{
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+ struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
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+ struct console *con = ctxt->console;
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+ struct nbcon_state cur;
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+
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+ while (!nbcon_context_try_acquire(ctxt))
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+ cpu_relax();
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+
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+ wctxt->outbuf = NULL;
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+ wctxt->len = 0;
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+ nbcon_state_read(con, &cur);
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+ wctxt->unsafe_takeover = cur.unsafe_takeover;
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+}
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+EXPORT_SYMBOL_GPL(nbcon_reacquire);
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+
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/**
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* nbcon_emit_next_record - Emit a record in the acquired context
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* @wctxt: The write context that will be handed to the write function
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--
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2.43.2
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