diff options
Diffstat (limited to 'debian/patches-rt/0079-printk-nbcon-Add-ownership-state-functions.patch')
| -rw-r--r-- | debian/patches-rt/0079-printk-nbcon-Add-ownership-state-functions.patch | 179 |
1 files changed, 179 insertions, 0 deletions
diff --git a/debian/patches-rt/0079-printk-nbcon-Add-ownership-state-functions.patch b/debian/patches-rt/0079-printk-nbcon-Add-ownership-state-functions.patch new file mode 100644 index 000000000..e26a5f332 --- /dev/null +++ b/debian/patches-rt/0079-printk-nbcon-Add-ownership-state-functions.patch @@ -0,0 +1,179 @@ +From: Thomas Gleixner <tglx@linutronix.de> +Date: Sat, 16 Sep 2023 21:26:04 +0206 +Subject: [PATCH 079/134] printk: nbcon: Add ownership state functions +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz + +Provide functions that are related to the safe handover mechanism +and allow console drivers to dynamically specify unsafe regions: + + - nbcon_context_can_proceed() + + Invoked by a console owner to check whether a handover request + is pending or whether the console has been taken over by another + context. If a handover request is pending, this function will + also perform the handover, thus cancelling its own ownership. + + - nbcon_context_enter_unsafe()/nbcon_context_exit_unsafe() + + Invoked by a console owner to denote that the driver is about + to enter or leave a critical region where a take over is unsafe. + The exit variant is the point where the current owner releases + the lock for a higher priority context which asked for the + friendly handover. + + The unsafe state is stored in the console state and allows a + new context to make informed decisions whether to attempt a + takeover of such a console. The unsafe state is also available + to the driver so that it can make informed decisions about the + required actions and possibly take a special emergency path. + +Co-developed-by: John Ogness <john.ogness@linutronix.de> +Signed-off-by: John Ogness <john.ogness@linutronix.de> +Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de> +Reviewed-by: Petr Mladek <pmladek@suse.com> +Signed-off-by: Petr Mladek <pmladek@suse.com> +Link: https://lore.kernel.org/r/20230916192007.608398-6-john.ogness@linutronix.de +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/printk/nbcon.c | 123 +++++++++++++++++++++++++++++++++++++++++++++++++- + 1 file changed, 122 insertions(+), 1 deletion(-) + +--- a/kernel/printk/nbcon.c ++++ b/kernel/printk/nbcon.c +@@ -537,7 +537,6 @@ static bool nbcon_owner_matches(struct n + * nbcon_context_release - Release the console + * @ctxt: The nbcon context from nbcon_context_try_acquire() + */ +-__maybe_unused + static void nbcon_context_release(struct nbcon_context *ctxt) + { + unsigned int cpu = smp_processor_id(); +@@ -566,6 +565,128 @@ static void nbcon_context_release(struct + } + + /** ++ * nbcon_context_can_proceed - Check whether ownership can proceed ++ * @ctxt: The nbcon context from nbcon_context_try_acquire() ++ * @cur: The current console state ++ * ++ * Return: True if this context still owns the console. False if ++ * ownership was handed over or taken. ++ * ++ * Must be invoked when entering the unsafe state to make sure that it still ++ * owns the lock. Also must be invoked when exiting the unsafe context ++ * to eventually free the lock for a higher priority context which asked ++ * for the friendly handover. ++ * ++ * It can be called inside an unsafe section when the console is just ++ * temporary in safe state instead of exiting and entering the unsafe ++ * state. ++ * ++ * Also it can be called in the safe context before doing an expensive ++ * safe operation. It does not make sense to do the operation when ++ * a higher priority context took the lock. ++ * ++ * When this function returns false then the calling context no longer owns ++ * the console and is no longer allowed to go forward. In this case it must ++ * back out immediately and carefully. The buffer content is also no longer ++ * trusted since it no longer belongs to the calling context. ++ */ ++static bool nbcon_context_can_proceed(struct nbcon_context *ctxt, struct nbcon_state *cur) ++{ ++ unsigned int cpu = smp_processor_id(); ++ ++ /* Make sure this context still owns the console. */ ++ if (!nbcon_owner_matches(cur, cpu, ctxt->prio)) ++ return false; ++ ++ /* The console owner can proceed if there is no waiter. */ ++ if (cur->req_prio == NBCON_PRIO_NONE) ++ return true; ++ ++ /* ++ * A console owner within an unsafe region is always allowed to ++ * proceed, even if there are waiters. It can perform a handover ++ * when exiting the unsafe region. Otherwise the waiter will ++ * need to perform an unsafe hostile takeover. ++ */ ++ if (cur->unsafe) ++ return true; ++ ++ /* Waiters always have higher priorities than owners. */ ++ WARN_ON_ONCE(cur->req_prio <= cur->prio); ++ ++ /* ++ * Having a safe point for take over and eventually a few ++ * duplicated characters or a full line is way better than a ++ * hostile takeover. Post processing can take care of the garbage. ++ * Release and hand over. ++ */ ++ nbcon_context_release(ctxt); ++ ++ /* ++ * It is not clear whether the waiter really took over ownership. The ++ * outermost callsite must make the final decision whether console ++ * ownership is needed for it to proceed. If yes, it must reacquire ++ * ownership (possibly hostile) before carefully proceeding. ++ * ++ * The calling context no longer owns the console so go back all the ++ * way instead of trying to implement reacquire heuristics in tons of ++ * places. ++ */ ++ return false; ++} ++ ++#define nbcon_context_enter_unsafe(c) __nbcon_context_update_unsafe(c, true) ++#define nbcon_context_exit_unsafe(c) __nbcon_context_update_unsafe(c, false) ++ ++/** ++ * __nbcon_context_update_unsafe - Update the unsafe bit in @con->nbcon_state ++ * @ctxt: The nbcon context from nbcon_context_try_acquire() ++ * @unsafe: The new value for the unsafe bit ++ * ++ * Return: True if the unsafe state was updated and this context still ++ * owns the console. Otherwise false if ownership was handed ++ * over or taken. ++ * ++ * This function allows console owners to modify the unsafe status of the ++ * console. ++ * ++ * When this function returns false then the calling context no longer owns ++ * the console and is no longer allowed to go forward. In this case it must ++ * back out immediately and carefully. The buffer content is also no longer ++ * trusted since it no longer belongs to the calling context. ++ * ++ * Internal helper to avoid duplicated code. ++ */ ++__maybe_unused ++static bool __nbcon_context_update_unsafe(struct nbcon_context *ctxt, bool unsafe) ++{ ++ struct console *con = ctxt->console; ++ struct nbcon_state cur; ++ struct nbcon_state new; ++ ++ nbcon_state_read(con, &cur); ++ ++ do { ++ /* ++ * The unsafe bit must not be cleared if an ++ * unsafe hostile takeover has occurred. ++ */ ++ if (!unsafe && cur.unsafe_takeover) ++ goto out; ++ ++ if (!nbcon_context_can_proceed(ctxt, &cur)) ++ return false; ++ ++ new.atom = cur.atom; ++ new.unsafe = unsafe; ++ } while (!nbcon_state_try_cmpxchg(con, &cur, &new)); ++ ++ cur.atom = new.atom; ++out: ++ return nbcon_context_can_proceed(ctxt, &cur); ++} ++ ++/** + * nbcon_alloc - Allocate buffers needed by the nbcon console + * @con: Console to allocate buffers for + * |