From d6b399a0e02a9063a5812af6cb8b657a4a1ecf68 Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Fri, 5 Mar 2021 13:19:56 +0100 Subject: um: time-travel/signals: fix ndelay() in interrupt We should be able to ndelay() from any context, even from an interrupt context! However, this is broken (not functionally, but locking-wise) in time-travel because we'll get into the time-travel code and enable interrupts to handle messages on other time-travel aware subsystems (only virtio for now). Luckily, I've already reworked the time-travel aware signal (interrupt) delivery for suspend/resume to have a time travel handler, which runs directly in the context of the signal and not from the Linux interrupt. In order to fix this time-travel issue then, we need to do a few things: 1) rework the signal handling code to call time-travel handlers (only) if interrupts are disabled but signals aren't blocked, instead of marking it only pending there. This is needed to not deadlock other communication. 2) rework time-travel to not enable interrupts while it's waiting for a message; 3) rework time-travel to not (just) disable interrupts but rather block signals at a lower level while it needs them disabled for communicating with the controller. Finally, since now we can actually spend even virtual time in interrupts-disabled sections, the delay warning when we deliver a time-travel delayed interrupt is no longer valid, things can (and should) now get delayed. Signed-off-by: Johannes Berg Signed-off-by: Richard Weinberger --- arch/um/include/shared/irq_user.h | 1 + arch/um/include/shared/os.h | 3 +++ arch/um/kernel/irq.c | 35 ++++++++++++++++++++----- arch/um/kernel/time.c | 35 +++++++++---------------- arch/um/os-Linux/signal.c | 55 ++++++++++++++++++++++++++++++++++++--- 5 files changed, 96 insertions(+), 33 deletions(-) (limited to 'arch/um') diff --git a/arch/um/include/shared/irq_user.h b/arch/um/include/shared/irq_user.h index 07239e801a5b..065829f443ae 100644 --- a/arch/um/include/shared/irq_user.h +++ b/arch/um/include/shared/irq_user.h @@ -17,6 +17,7 @@ enum um_irq_type { struct siginfo; extern void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs); +void sigio_run_timetravel_handlers(void); extern void free_irq_by_fd(int fd); extern void deactivate_fd(int fd, int irqnum); extern int deactivate_all_fds(void); diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h index f9fbbddc38bb..453b13369533 100644 --- a/arch/um/include/shared/os.h +++ b/arch/um/include/shared/os.h @@ -242,6 +242,9 @@ extern int set_signals_trace(int enable); extern int os_is_signal_stack(void); extern void deliver_alarm(void); extern void register_pm_wake_signal(void); +extern void block_signals_hard(void); +extern void unblock_signals_hard(void); +extern void mark_sigio_pending(void); /* util.c */ extern void stack_protections(unsigned long address); diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c index 82af5191e73d..1c448ea4729e 100644 --- a/arch/um/kernel/irq.c +++ b/arch/um/kernel/irq.c @@ -123,7 +123,8 @@ static bool irq_do_timetravel_handler(struct irq_entry *entry, #endif static void sigio_reg_handler(int idx, struct irq_entry *entry, enum um_irq_type t, - struct uml_pt_regs *regs) + struct uml_pt_regs *regs, + bool timetravel_handlers_only) { struct irq_reg *reg = &entry->reg[t]; @@ -136,18 +137,29 @@ static void sigio_reg_handler(int idx, struct irq_entry *entry, enum um_irq_type if (irq_do_timetravel_handler(entry, t)) return; - if (irqs_suspended) + /* + * If we're called to only run time-travel handlers then don't + * actually proceed but mark sigio as pending (if applicable). + * For suspend/resume, timetravel_handlers_only may be true + * despite time-travel not being configured and used. + */ + if (timetravel_handlers_only) { +#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT + mark_sigio_pending(); +#endif return; + } irq_io_loop(reg, regs); } -void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs) +static void _sigio_handler(struct uml_pt_regs *regs, + bool timetravel_handlers_only) { struct irq_entry *irq_entry; int n, i; - if (irqs_suspended && !um_irq_timetravel_handler_used()) + if (timetravel_handlers_only && !um_irq_timetravel_handler_used()) return; while (1) { @@ -172,14 +184,20 @@ void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs) irq_entry = os_epoll_get_data_pointer(i); for (t = 0; t < NUM_IRQ_TYPES; t++) - sigio_reg_handler(i, irq_entry, t, regs); + sigio_reg_handler(i, irq_entry, t, regs, + timetravel_handlers_only); } } - if (!irqs_suspended) + if (!timetravel_handlers_only) free_irqs(); } +void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs) +{ + _sigio_handler(regs, irqs_suspended); +} + static struct irq_entry *get_irq_entry_by_fd(int fd) { struct irq_entry *walk; @@ -467,6 +485,11 @@ int um_request_irq_tt(int irq, int fd, enum um_irq_type type, devname, dev_id, timetravel_handler); } EXPORT_SYMBOL(um_request_irq_tt); + +void sigio_run_timetravel_handlers(void) +{ + _sigio_handler(NULL, true); +} #endif #ifdef CONFIG_PM_SLEEP diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c index e0cdb9694fb8..fddd1dec27e6 100644 --- a/arch/um/kernel/time.c +++ b/arch/um/kernel/time.c @@ -68,23 +68,15 @@ static void time_travel_handle_message(struct um_timetravel_msg *msg, int ret; /* - * Poll outside the locked section (if we're not called to only read - * the response) so we can get interrupts for e.g. virtio while we're - * here, but then we need to lock to not get interrupted between the - * read of the message and write of the ACK. + * We can't unlock here, but interrupt signals with a timetravel_handler + * (see um_request_irq_tt) get to the timetravel_handler anyway. */ if (mode != TTMH_READ) { - bool disabled = irqs_disabled(); + BUG_ON(mode == TTMH_IDLE && !irqs_disabled()); - BUG_ON(mode == TTMH_IDLE && !disabled); - - if (disabled) - local_irq_enable(); while (os_poll(1, &time_travel_ext_fd) != 0) { /* nothing */ } - if (disabled) - local_irq_disable(); } ret = os_read_file(time_travel_ext_fd, msg, sizeof(*msg)); @@ -123,15 +115,15 @@ static u64 time_travel_ext_req(u32 op, u64 time) .time = time, .seq = mseq, }; - unsigned long flags; /* - * We need to save interrupts here and only restore when we - * got the ACK - otherwise we can get interrupted and send - * another request while we're still waiting for an ACK, but - * the peer doesn't know we got interrupted and will send - * the ACKs in the same order as the message, but we'd need - * to see them in the opposite order ... + * We need to block even the timetravel handlers of SIGIO here and + * only restore their use when we got the ACK - otherwise we may + * (will) get interrupted by that, try to queue the IRQ for future + * processing and thus send another request while we're still waiting + * for an ACK, but the peer doesn't know we got interrupted and will + * send the ACKs in the same order as the message, but we'd need to + * see them in the opposite order ... * * This wouldn't matter *too* much, but some ACKs carry the * current time (for UM_TIMETRAVEL_GET) and getting another @@ -140,7 +132,7 @@ static u64 time_travel_ext_req(u32 op, u64 time) * The sequence number assignment that happens here lets us * debug such message handling issues more easily. */ - local_irq_save(flags); + block_signals_hard(); os_write_file(time_travel_ext_fd, &msg, sizeof(msg)); while (msg.op != UM_TIMETRAVEL_ACK) @@ -152,7 +144,7 @@ static u64 time_travel_ext_req(u32 op, u64 time) if (op == UM_TIMETRAVEL_GET) time_travel_set_time(msg.time); - local_irq_restore(flags); + unblock_signals_hard(); return msg.time; } @@ -352,9 +344,6 @@ void deliver_time_travel_irqs(void) while ((e = list_first_entry_or_null(&time_travel_irqs, struct time_travel_event, list))) { - WARN(e->time != time_travel_time, - "time moved from %lld to %lld before IRQ delivery\n", - time_travel_time, e->time); list_del(&e->list); e->pending = false; e->fn(e); diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c index 8c9d162e6c51..1d501acb22ee 100644 --- a/arch/um/os-Linux/signal.c +++ b/arch/um/os-Linux/signal.c @@ -18,6 +18,7 @@ #include #include #include +#include void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = { [SIGTRAP] = relay_signal, @@ -63,16 +64,29 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc) #define SIGALRM_MASK (1 << SIGALRM_BIT) int signals_enabled; +#ifdef UML_CONFIG_UML_TIME_TRAVEL_SUPPORT +static int signals_blocked; +#else +#define signals_blocked false +#endif static unsigned int signals_pending; static unsigned int signals_active = 0; void sig_handler(int sig, struct siginfo *si, mcontext_t *mc) { - int enabled; + int enabled = signals_enabled; - enabled = signals_enabled; - if (!enabled && (sig == SIGIO)) { - signals_pending |= SIGIO_MASK; + if ((signals_blocked || !enabled) && (sig == SIGIO)) { + /* + * In TT_MODE_EXTERNAL, need to still call time-travel + * handlers unless signals are also blocked for the + * external time message processing. This will mark + * signals_pending by itself (only if necessary.) + */ + if (!signals_blocked && time_travel_mode == TT_MODE_EXTERNAL) + sigio_run_timetravel_handlers(); + else + signals_pending |= SIGIO_MASK; return; } @@ -363,6 +377,39 @@ int set_signals_trace(int enable) return ret; } +#ifdef UML_CONFIG_UML_TIME_TRAVEL_SUPPORT +void mark_sigio_pending(void) +{ + signals_pending |= SIGIO_MASK; +} + +void block_signals_hard(void) +{ + if (signals_blocked) + return; + signals_blocked = 1; + barrier(); +} + +void unblock_signals_hard(void) +{ + if (!signals_blocked) + return; + /* Must be set to 0 before we check the pending bits etc. */ + signals_blocked = 0; + barrier(); + + if (signals_pending && signals_enabled) { + /* this is a bit inefficient, but that's not really important */ + block_signals(); + unblock_signals(); + } else if (signals_pending & SIGIO_MASK) { + /* we need to run time-travel handlers even if not enabled */ + sigio_run_timetravel_handlers(); + } +} +#endif + int os_is_signal_stack(void) { stack_t ss; -- cgit v1.2.3