From f9dfe31c7f5af92e8e9cd2cf36bb67fab830c257 Mon Sep 17 00:00:00 2001 From: John Ogness Date: Fri, 20 Oct 2023 10:01:58 +0000 Subject: [PATCH 146/184] printk: nbcon: Provide function to reacquire ownership Contexts may become nbcon owners for various reasons, not just for printing. Indeed, the port->lock wrapper takes ownership for anything relating to the hardware. Since ownership can be lost at any time due to handover or takeover, a context _should_ be prepared. However, there are many scenarios where the context _must_ reacquire ownership in order to finish what it started. One such example is when interrupts are disabled by a context. No other context will automagically re-enable the interrupts. For this case, the disabling context _must_ reacquire nbcon ownership so that it can re-enable the interrupts. Provide nbcon_reacquire() for exactly this purpose. Note that for printing contexts, after a successful reacquire the context will have no output buffer because that has been lost. nbcon_reacquire() cannot be used to resume printing. Signed-off-by: John Ogness Signed-off-by: Sebastian Andrzej Siewior --- include/linux/console.h | 2 ++ kernel/printk/nbcon.c | 16 ++++++++++++++++ 2 files changed, 18 insertions(+) diff --git a/include/linux/console.h b/include/linux/console.h index 663cd74fc4bc..87e787ffb653 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -472,12 +472,14 @@ extern void nbcon_cpu_emergency_exit(void); extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt); extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt); extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt); +extern void nbcon_reacquire(struct nbcon_write_context *wctxt); #else static inline void nbcon_cpu_emergency_enter(void) { } static inline void nbcon_cpu_emergency_exit(void) { } static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; } static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; } static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; } +static inline void nbcon_reacquire(struct nbcon_write_context *wctxt) { } #endif extern int console_set_on_cmdline; diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index b2deb902bc0f..427e26c89067 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -867,6 +867,22 @@ bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) } EXPORT_SYMBOL_GPL(nbcon_exit_unsafe); +void nbcon_reacquire(struct nbcon_write_context *wctxt) +{ + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); + struct console *con = ctxt->console; + struct nbcon_state cur; + + while (!nbcon_context_try_acquire(ctxt)) + cpu_relax(); + + wctxt->outbuf = NULL; + wctxt->len = 0; + nbcon_state_read(con, &cur); + wctxt->unsafe_takeover = cur.unsafe_takeover; +} +EXPORT_SYMBOL_GPL(nbcon_reacquire); + /** * nbcon_emit_next_record - Emit a record in the acquired context * @wctxt: The write context that will be handed to the write function -- 2.34.1