source: src/libcfa/concurrency/preemption.c@ 4a333d35

ADT aaron-thesis arm-eh ast-experimental cleanup-dtors deferred_resn demangler enum forall-pointer-decay jacob/cs343-translation jenkins-sandbox new-ast new-ast-unique-expr new-env no_list persistent-indexer pthread-emulation qualifiedEnum with_gc
Last change on this file since 4a333d35 was a83ffa4, checked in by Thierry Delisle <tdelisle@…>, 7 years ago

Preemption now properly restore signal before context switching
  • Property mode set to 100644
File size: 15.1 KB
Line 
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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