source: src/libcfa/concurrency/preemption.c @ a83ffa4

aaron-thesisarm-ehcleanup-dtorsdeferred_resndemanglerjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-exprnew-envno_listpersistent-indexerwith_gc
Last change on this file since a83ffa4 was a83ffa4, checked in by Thierry Delisle <tdelisle@…>, 4 years ago

Preemption now properly restore signal before context switching

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1//
2// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
3//
4// The contents of this file are covered under the licence agreement in the
5// file "LICENCE" distributed with Cforall.
6//
7// signal.c --
8//
9// Author           : Thierry Delisle
10// Created On       : Mon Jun 5 14:20:42 2017
11// Last Modified By : Peter A. Buhr
12// Last Modified On : Mon Apr  9 13:52:39 2018
13// Update Count     : 36
14//
15
16#include "preemption.h"
17#include <assert.h>
18
19extern "C" {
20#include <errno.h>
21#include <stdio.h>
22#include <string.h>
23#include <unistd.h>
24}
25
26#include "bits/signal.h"
27
28#if !defined(__CFA_DEFAULT_PREEMPTION__)
29#define __CFA_DEFAULT_PREEMPTION__ 10`ms
30#endif
31
32Duration default_preemption() __attribute__((weak)) {
33        return __CFA_DEFAULT_PREEMPTION__;
34}
35
36// FwdDeclarations : timeout handlers
37static void preempt( processor   * this );
38static void timeout( thread_desc * this );
39
40// FwdDeclarations : Signal handlers
41void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
42void sigHandler_segv     ( __CFA_SIGPARMS__ );
43void sigHandler_ill      ( __CFA_SIGPARMS__ );
44void sigHandler_fpe      ( __CFA_SIGPARMS__ );
45void sigHandler_abort    ( __CFA_SIGPARMS__ );
46
47// FwdDeclarations : alarm thread main
48void * alarm_loop( __attribute__((unused)) void * args );
49
50// Machine specific register name
51#if   defined( __i386 )
52#define CFA_REG_IP gregs[REG_EIP]
53#elif defined( __x86_64 )
54#define CFA_REG_IP gregs[REG_RIP]
55#elif defined( __ARM_ARCH )
56#define CFA_REG_IP arm_pc
57#else
58#error unknown hardware architecture
59#endif
60
61KERNEL_STORAGE(event_kernel_t, event_kernel);         // private storage for event kernel
62event_kernel_t * event_kernel;                        // kernel public handle to even kernel
63static pthread_t alarm_thread;                        // pthread handle to alarm thread
64
65void ?{}(event_kernel_t & this) with( this ) {
66        alarms{};
67        lock{};
68}
69
70enum {
71        PREEMPT_NORMAL    = 0,
72        PREEMPT_TERMINATE = 1,
73};
74
75//=============================================================================================
76// Kernel Preemption logic
77//=============================================================================================
78
79// Get next expired node
80static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
81        if( !alarms->head ) return NULL;                          // If no alarms return null
82        if( alarms->head->alarm >= currtime ) return NULL;        // If alarms head not expired return null
83        return pop(alarms);                                       // Otherwise just pop head
84}
85
86// Tick one frame of the Discrete Event Simulation for alarms
87void tick_preemption() {
88        alarm_node_t * node = NULL;                     // Used in the while loop but cannot be declared in the while condition
89        alarm_list_t * alarms = &event_kernel->alarms;  // Local copy for ease of reading
90        Time currtime = __kernel_get_time();                    // Check current time once so we everything "happens at once"
91
92        //Loop throught every thing expired
93        while( node = get_expired( alarms, currtime ) ) {
94                // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
95
96                // Check if this is a kernel
97                if( node->kernel_alarm ) {
98                        preempt( node->proc );
99                }
100                else {
101                        timeout( node->thrd );
102                }
103
104                // Check if this is a periodic alarm
105                Duration period = node->period;
106                if( period > 0 ) {
107                        // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
108                        node->alarm = currtime + period;    // Alarm is periodic, add currtime to it (used cached current time)
109                        insert( alarms, node );             // Reinsert the node for the next time it triggers
110                }
111                else {
112                        node->set = false;                  // Node is one-shot, just mark it as not pending
113                }
114        }
115
116        // If there are still alarms pending, reset the timer
117        if( alarms->head ) {
118                __cfaabi_dbg_print_buffer_decl( " KERNEL: @%lu(%lu) resetting alarm to %lu.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
119                Duration delta = alarms->head->alarm - currtime;
120                Duration caped = max(delta, 50`us);
121                // itimerval tim  = { caped };
122                // __cfaabi_dbg_print_buffer_local( "    Values are %lu, %lu, %lu %lu.\n", delta.tv, caped.tv, tim.it_value.tv_sec, tim.it_value.tv_usec);
123
124                __kernel_set_timer( caped );
125        }
126}
127
128// Update the preemption of a processor and notify interested parties
129void update_preemption( processor * this, Duration duration ) {
130        alarm_node_t * alarm = this->preemption_alarm;
131
132        // Alarms need to be enabled
133        if ( duration > 0 && ! alarm->set ) {
134                alarm->alarm = __kernel_get_time() + duration;
135                alarm->period = duration;
136                register_self( alarm );
137        }
138        // Zero duration but alarm is set
139        else if ( duration == 0 && alarm->set ) {
140                unregister_self( alarm );
141                alarm->alarm = 0;
142                alarm->period = 0;
143        }
144        // If alarm is different from previous, change it
145        else if ( duration > 0 && alarm->period != duration ) {
146                unregister_self( alarm );
147                alarm->alarm = __kernel_get_time() + duration;
148                alarm->period = duration;
149                register_self( alarm );
150        }
151}
152
153//=============================================================================================
154// Kernel Signal Tools
155//=============================================================================================
156
157__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
158
159extern "C" {
160        // Disable interrupts by incrementing the counter
161        void disable_interrupts() {
162                with( kernelTLS.preemption_state ) {
163                        enabled = false;
164                        __attribute__((unused)) unsigned short new_val = disable_count + 1;
165                        disable_count = new_val;
166                        verify( new_val < 65_000u );              // If this triggers someone is disabling interrupts without enabling them
167                }
168        }
169
170        // Enable interrupts by decrementing the counter
171        // If counter reaches 0, execute any pending CtxSwitch
172        void enable_interrupts( __cfaabi_dbg_ctx_param ) {
173                processor   * proc = kernelTLS.this_processor; // Cache the processor now since interrupts can start happening after the atomic add
174                thread_desc * thrd = kernelTLS.this_thread;       // Cache the thread now since interrupts can start happening after the atomic add
175
176                with( kernelTLS.preemption_state ){
177                        unsigned short prev = disable_count;
178                        disable_count -= 1;
179                        verify( prev != 0u );                     // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
180
181                        // Check if we need to prempt the thread because an interrupt was missed
182                        if( prev == 1 ) {
183                                enabled = true;
184                                if( proc->pending_preemption ) {
185                                        proc->pending_preemption = false;
186                                        BlockInternal( thrd );
187                                }
188                        }
189                }
190
191                // For debugging purposes : keep track of the last person to enable the interrupts
192                __cfaabi_dbg_debug_do( proc->last_enable = caller; )
193        }
194
195        // Disable interrupts by incrementint the counter
196        // Don't execute any pending CtxSwitch even if counter reaches 0
197        void enable_interrupts_noPoll() {
198                unsigned short prev = kernelTLS.preemption_state.disable_count;
199                kernelTLS.preemption_state.disable_count -= 1;
200                verifyf( prev != 0u, "Incremented from %u\n", prev );                     // If this triggers someone is enabled already enabled interrupts
201                if( prev == 1 ) {
202                        kernelTLS.preemption_state.enabled = true;
203                }
204        }
205}
206
207// sigprocmask wrapper : unblock a single signal
208static inline void signal_unblock( int sig ) {
209        sigset_t mask;
210        sigemptyset( &mask );
211        sigaddset( &mask, sig );
212
213        if ( pthread_sigmask( SIG_UNBLOCK, &mask, NULL ) == -1 ) {
214            abort( "internal error, pthread_sigmask" );
215        }
216}
217
218// sigprocmask wrapper : block a single signal
219static inline void signal_block( int sig ) {
220        sigset_t mask;
221        sigemptyset( &mask );
222        sigaddset( &mask, sig );
223
224        if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
225            abort( "internal error, pthread_sigmask" );
226        }
227}
228
229// kill wrapper : signal a processor
230static void preempt( processor * this ) {
231        sigval_t value = { PREEMPT_NORMAL };
232        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
233}
234
235// kill wrapper : signal a processor
236void terminate(processor * this) {
237        this->do_terminate = true;
238        sigval_t value = { PREEMPT_TERMINATE };
239        pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
240}
241
242// reserved for future use
243static void timeout( thread_desc * this ) {
244        //TODO : implement waking threads
245}
246
247// KERNEL ONLY
248// Check if a CtxSwitch signal handler shoud defer
249// If true  : preemption is safe
250// If false : preemption is unsafe and marked as pending
251static inline bool preemption_ready() {
252        // Check if preemption is safe
253        bool ready = kernelTLS.preemption_state.enabled && ! kernelTLS.preemption_state.in_progress;
254
255        // Adjust the pending flag accordingly
256        kernelTLS.this_processor->pending_preemption = !ready;
257        return ready;
258}
259
260//=============================================================================================
261// Kernel Signal Startup/Shutdown logic
262//=============================================================================================
263
264// Startup routine to activate preemption
265// Called from kernel_startup
266void kernel_start_preemption() {
267        __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
268
269        // Start with preemption disabled until ready
270        kernelTLS.preemption_state.enabled = false;
271        kernelTLS.preemption_state.disable_count = 1;
272
273        // Initialize the event kernel
274        event_kernel = (event_kernel_t *)&storage_event_kernel;
275        (*event_kernel){};
276
277        // Setup proper signal handlers
278        __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART );         // CtxSwitch handler
279
280        signal_block( SIGALRM );
281
282        pthread_create( &alarm_thread, NULL, alarm_loop, NULL );
283}
284
285// Shutdown routine to deactivate preemption
286// Called from kernel_shutdown
287void kernel_stop_preemption() {
288        __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
289
290        // Block all signals since we are already shutting down
291        sigset_t mask;
292        sigfillset( &mask );
293        sigprocmask( SIG_BLOCK, &mask, NULL );
294
295        // Notify the alarm thread of the shutdown
296        sigval val = { 1 };
297        pthread_sigqueue( alarm_thread, SIGALRM, val );
298
299        // Wait for the preemption thread to finish
300        pthread_join( alarm_thread, NULL );
301
302        // Preemption is now fully stopped
303
304        __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
305}
306
307// Raii ctor/dtor for the preemption_scope
308// Used by thread to control when they want to receive preemption signals
309void ?{}( preemption_scope & this, processor * proc ) {
310        (this.alarm){ proc, (Time){ 0 }, 0`s };
311        this.proc = proc;
312        this.proc->preemption_alarm = &this.alarm;
313
314        update_preemption( this.proc, this.proc->cltr->preemption_rate );
315}
316
317void ^?{}( preemption_scope & this ) {
318        disable_interrupts();
319
320        update_preemption( this.proc, 0`s );
321}
322
323//=============================================================================================
324// Kernel Signal Handlers
325//=============================================================================================
326
327// Context switch signal handler
328// Receives SIGUSR1 signal and causes the current thread to yield
329void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
330        __cfaabi_dbg_debug_do( last_interrupt = (void *)(cxt->uc_mcontext.CFA_REG_IP); )
331
332        // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
333        // the interrupt that is supposed to force the kernel thread to preempt might arrive
334        // before the kernel thread has even started running. When that happens an iterrupt
335        // we a null 'this_processor' will be caught, just ignore it.
336        if(! kernelTLS.this_processor ) return;
337
338        choose(sfp->si_value.sival_int) {
339                case PREEMPT_NORMAL   : ;// Normal case, nothing to do here
340                case PREEMPT_TERMINATE: verify( kernelTLS.this_processor->do_terminate);
341                default:
342                        abort( "internal error, signal value is %d", sfp->si_value.sival_int );
343        }
344
345        // Check if it is safe to preempt here
346        if( !preemption_ready() ) { return; }
347
348        __cfaabi_dbg_print_buffer_decl( " KERNEL: preempting core %p (%p @ %p).\n", kernelTLS.this_processor, kernelTLS.this_thread, (void *)(cxt->uc_mcontext.CFA_REG_IP) );
349
350        // Sync flag : prevent recursive calls to the signal handler
351        kernelTLS.preemption_state.in_progress = true;
352
353        // Clear sighandler mask before context switching.
354        static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
355        if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), NULL ) == -1 ) {
356                abort( "internal error, sigprocmask" );
357        }
358
359        // TODO: this should go in finish action
360        // Clear the in progress flag
361        kernelTLS.preemption_state.in_progress = false;
362
363        // Preemption can occur here
364
365        BlockInternal( kernelTLS.this_thread ); // Do the actual CtxSwitch
366}
367
368// Main of the alarm thread
369// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
370void * alarm_loop( __attribute__((unused)) void * args ) {
371        // Block sigalrms to control when they arrive
372        sigset_t mask;
373        sigfillset(&mask);
374        if ( pthread_sigmask( SIG_BLOCK, &mask, NULL ) == -1 ) {
375            abort( "internal error, pthread_sigmask" );
376        }
377
378        sigemptyset( &mask );
379        sigaddset( &mask, SIGALRM );
380
381        // Main loop
382        while( true ) {
383                // Wait for a sigalrm
384                siginfo_t info;
385                int sig = sigwaitinfo( &mask, &info );
386
387                if( sig < 0 ) {
388                        //Error!
389                        int err = errno;
390                        switch( err ) {
391                                case EAGAIN :
392                                case EINTR :
393                                        {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
394                                        continue;
395                        case EINVAL :
396                                        abort( "Timeout was invalid." );
397                                default:
398                                        abort( "Unhandled error %d", err);
399                        }
400                }
401
402                // If another signal arrived something went wrong
403                assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
404
405                // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
406                // Switch on the code (a.k.a. the sender) to
407                switch( info.si_code )
408                {
409                // Timers can apparently be marked as sent for the kernel
410                // In either case, tick preemption
411                case SI_TIMER:
412                case SI_KERNEL:
413                        // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
414                        lock( event_kernel->lock __cfaabi_dbg_ctx2 );
415                        tick_preemption();
416                        unlock( event_kernel->lock );
417                        break;
418                // Signal was not sent by the kernel but by an other thread
419                case SI_QUEUE:
420                        // For now, other thread only signal the alarm thread to shut it down
421                        // If this needs to change use info.si_value and handle the case here
422                        goto EXIT;
423                }
424        }
425
426EXIT:
427        __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
428        return NULL;
429}
430
431//=============================================================================================
432// Kernel Signal Debug
433//=============================================================================================
434
435void __cfaabi_check_preemption() {
436        bool ready = kernelTLS.preemption_state.enabled;
437        if(!ready) { abort("Preemption should be ready"); }
438
439        sigset_t oldset;
440        int ret;
441        ret = pthread_sigmask(0, NULL, &oldset);
442        if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
443
444        ret = sigismember(&oldset, SIGUSR1);
445        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
446        if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
447
448        ret = sigismember(&oldset, SIGALRM);
449        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
450        if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
451
452        ret = sigismember(&oldset, SIGTERM);
453        if(ret <  0) { abort("ERROR sigismember returned %d", ret); }
454        if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
455}
456
457// Local Variables: //
458// mode: c //
459// tab-width: 4 //
460// End: //
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