source: libcfa/src/concurrency/preemption.cfa@ 0d4456b

ADT arm-eh ast-experimental enum forall-pointer-decay jacob/cs343-translation new-ast-unique-expr pthread-emulation qualifiedEnum
Last change on this file since 0d4456b was 82a2fed, checked in by Thierry Delisle <tdelisle@…>, 5 years ago

Changed preemption to use code sections rather than atomic access to TLS.
  • Property mode set to 100644
File size: 25.0 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 : Fri Nov 6 07:42:13 2020
13// Update Count : 54
14//
15
16#define __cforall_thread__
17
18#include "preemption.hfa"
19#include <assert.h>
20
21#include <errno.h>
22#include <stdio.h>
23#include <string.h>
24#include <unistd.h>
25#include <limits.h> // PTHREAD_STACK_MIN
26
27#include "bits/signal.hfa"
28#include "kernel_private.hfa"
29
30#if !defined(__CFA_DEFAULT_PREEMPTION__)
31#define __CFA_DEFAULT_PREEMPTION__ 10`ms
32#endif
33
34Duration default_preemption() __attribute__((weak)) {
35 return __CFA_DEFAULT_PREEMPTION__;
36}
37
38// FwdDeclarations : timeout handlers
39static void preempt( processor * this );
40static void timeout( $thread * this );
41
42// FwdDeclarations : Signal handlers
43static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
44static void sigHandler_alarm ( __CFA_SIGPARMS__ );
45static void sigHandler_segv ( __CFA_SIGPARMS__ );
46static void sigHandler_ill ( __CFA_SIGPARMS__ );
47static void sigHandler_fpe ( __CFA_SIGPARMS__ );
48static void sigHandler_abort ( __CFA_SIGPARMS__ );
49
50// FwdDeclarations : alarm thread main
51static void * alarm_loop( __attribute__((unused)) void * args );
52
53// Machine specific register name
54#if defined( __i386 )
55#define CFA_REG_IP gregs[REG_EIP]
56#elif defined( __x86_64 )
57#define CFA_REG_IP gregs[REG_RIP]
58#elif defined( __arm__ )
59#define CFA_REG_IP arm_pc
60#elif defined( __aarch64__ )
61#define CFA_REG_IP pc
62#else
63#error unsupported hardware architecture
64#endif
65
66KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
67event_kernel_t * event_kernel; // kernel public handle to even kernel
68static pthread_t alarm_thread; // pthread handle to alarm thread
69static void * alarm_stack; // pthread stack for alarm thread
70
71static void ?{}(event_kernel_t & this) with( this ) {
72 alarms{};
73 lock{};
74}
75
76enum {
77 PREEMPT_NORMAL = 0,
78 PREEMPT_TERMINATE = 1,
79};
80
81//=============================================================================================
82// Kernel Preemption logic
83//=============================================================================================
84
85// Get next expired node
86static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
87 if( ! & (*alarms)`first ) return 0p; // If no alarms return null
88 if( (*alarms)`first.alarm >= currtime ) return 0p; // If alarms head not expired return null
89 return pop(alarms); // Otherwise just pop head
90}
91
92// Tick one frame of the Discrete Event Simulation for alarms
93static void tick_preemption(void) {
94 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
95 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
96 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
97
98 //Loop throught every thing expired
99 while( node = get_expired( alarms, currtime ) ) {
100 // __cfaabi_dbg_print_buffer_decl( " KERNEL: preemption tick.\n" );
101 Duration period = node->period;
102 if( period == 0) {
103 node->set = false; // Node is one-shot, just mark it as not pending
104 }
105
106 // Check if this is a kernel
107 if( node->type == Kernel ) {
108 preempt( node->proc );
109 }
110 else if( node->type == User ) {
111 timeout( node->thrd );
112 }
113 else {
114 node->callback(*node);
115 }
116
117 // Check if this is a periodic alarm
118 if( period > 0 ) {
119 // __cfaabi_dbg_print_buffer_local( " KERNEL: alarm period is %lu.\n", period.tv );
120 node->alarm = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
121 insert( alarms, node ); // Reinsert the node for the next time it triggers
122 }
123 }
124
125 // If there are still alarms pending, reset the timer
126 if( & (*alarms)`first ) {
127 __cfadbg_print_buffer_decl(preemption, " KERNEL: @%ju(%ju) resetting alarm to %ju.\n", currtime.tv, __kernel_get_time().tv, (alarms->head->alarm - currtime).tv);
128 Duration delta = (*alarms)`first.alarm - currtime;
129 Duration capped = max(delta, 50`us);
130 // itimerval tim = { caped };
131 // __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);
132
133 __kernel_set_timer( capped );
134 }
135}
136
137// Update the preemption of a processor and notify interested parties
138void update_preemption( processor * this, Duration duration ) {
139 alarm_node_t * alarm = this->preemption_alarm;
140
141 // Alarms need to be enabled
142 if ( duration > 0 && ! alarm->set ) {
143 alarm->alarm = __kernel_get_time() + duration;
144 alarm->period = duration;
145 register_self( alarm );
146 }
147 // Zero duration but alarm is set
148 else if ( duration == 0 && alarm->set ) {
149 unregister_self( alarm );
150 alarm->alarm = 0;
151 alarm->period = 0;
152 }
153 // If alarm is different from previous, change it
154 else if ( duration > 0 && alarm->period != duration ) {
155 unregister_self( alarm );
156 alarm->alarm = __kernel_get_time() + duration;
157 alarm->period = duration;
158 register_self( alarm );
159 }
160}
161
162//=============================================================================================
163// Kernel Signal Tools
164//=============================================================================================
165// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
166//
167// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
168// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
169//
170// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
171//
172// _Thread_local volatile int interrupts;
173// int main() {
174// interrupts = 0; // disable interrupts }
175//
176// which generates the following code on the ARM
177//
178// (gdb) disassemble main
179// Dump of assembler code for function main:
180// 0x0000000000000610 <+0>: mrs x1, tpidr_el0
181// 0x0000000000000614 <+4>: mov w0, #0x0 // #0
182// 0x0000000000000618 <+8>: add x1, x1, #0x0, lsl #12
183// 0x000000000000061c <+12>: add x1, x1, #0x10
184// 0x0000000000000620 <+16>: str wzr, [x1]
185// 0x0000000000000624 <+20>: ret
186//
187// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1. Register w0 is set to 0. The two adds
188// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
189// "interrupts". Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
190// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
191// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
192// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
193// turning off interrupt on the wrong kernel thread.
194//
195// On the x86, the following code is generated for the same code fragment.
196//
197// (gdb) disassemble main
198// Dump of assembler code for function main:
199// 0x0000000000400420 <+0>: movl $0x0,%fs:0xfffffffffffffffc
200// 0x000000000040042c <+12>: xor %eax,%eax
201// 0x000000000040042e <+14>: retq
202//
203// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
204// register "fs".
205//
206// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
207// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
208//
209// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
210// thread on the same kernel thread.
211//
212// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
213// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
214// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
215// available.
216
217//----------
218// special case for preemption since used often
219bool __preemption_enabled() {
220 // create a assembler label before
221 // marked as clobber all to avoid movement
222 asm volatile("__cfaasm_check_before:":::"memory");
223
224 // access tls as normal
225 bool enabled = __cfaabi_tls.preemption_state.enabled;
226
227 // create a assembler label after
228 // marked as clobber all to avoid movement
229 asm volatile("__cfaasm_check_after:":::"memory");
230 return enabled;
231}
232
233struct asm_region {
234 void * before;
235 void * after;
236};
237
238static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
239 return ip >= region.before && ip <= region.after;
240}
241
242
243//----------
244// Get data from the TLS block
245// struct asm_region __cfaasm_get;
246uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
247uintptr_t __cfatls_get( unsigned long int offset ) {
248 // __cfaasm_get.before = ({ void * value; asm("movq $__cfaasm_get_before, %[v]\n\t" : [v]"=r"(value) ); value; });
249 // __cfaasm_get.after = ({ void * value; asm("movq $__cfaasm_get_after , %[v]\n\t" : [v]"=r"(value) ); value; });
250 // create a assembler label before
251 // marked as clobber all to avoid movement
252 asm volatile("__cfaasm_get_before:":::"memory");
253
254 // access tls as normal (except for pointer arithmetic)
255 uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
256
257 // create a assembler label after
258 // marked as clobber all to avoid movement
259 asm volatile("__cfaasm_get_after:":::"memory");
260 return val;
261}
262
263extern "C" {
264 // Disable interrupts by incrementing the counter
265 void disable_interrupts() {
266 // create a assembler label before
267 // marked as clobber all to avoid movement
268 asm volatile("__cfaasm_dsable_before:":::"memory");
269
270 with( __cfaabi_tls.preemption_state ) {
271 #if GCC_VERSION > 50000
272 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
273 #endif
274
275 // Set enabled flag to false
276 // should be atomic to avoid preemption in the middle of the operation.
277 // use memory order RELAXED since there is no inter-thread on this variable requirements
278 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
279
280 // Signal the compiler that a fence is needed but only for signal handlers
281 __atomic_signal_fence(__ATOMIC_ACQUIRE);
282
283 __attribute__((unused)) unsigned short new_val = disable_count + 1;
284 disable_count = new_val;
285 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
286 }
287
288 // create a assembler label after
289 // marked as clobber all to avoid movement
290 asm volatile("__cfaasm_dsable_after:":::"memory");
291 }
292
293 // Enable interrupts by decrementing the counter
294 // If counter reaches 0, execute any pending __cfactx_switch
295 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
296 // create a assembler label before
297 // marked as clobber all to avoid movement
298 asm volatile("__cfaasm_enble_before:":::"memory");
299
300 processor * proc = __cfaabi_tls.this_processor; // Cache the processor now since interrupts can start happening after the atomic store
301 /* paranoid */ verify( proc );
302
303 with( __cfaabi_tls.preemption_state ){
304 unsigned short prev = disable_count;
305 disable_count -= 1;
306 verify( prev != 0u ); // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
307
308 // Check if we need to prempt the thread because an interrupt was missed
309 if( prev == 1 ) {
310 #if GCC_VERSION > 50000
311 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
312 #endif
313
314 // Set enabled flag to true
315 // should be atomic to avoid preemption in the middle of the operation.
316 // use memory order RELAXED since there is no inter-thread on this variable requirements
317 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
318
319 // Signal the compiler that a fence is needed but only for signal handlers
320 __atomic_signal_fence(__ATOMIC_RELEASE);
321 if( proc->pending_preemption ) {
322 proc->pending_preemption = false;
323 force_yield( __POLL_PREEMPTION );
324 }
325 }
326 }
327
328 // For debugging purposes : keep track of the last person to enable the interrupts
329 __cfaabi_dbg_debug_do( proc->last_enable = caller; )
330
331 // create a assembler label after
332 // marked as clobber all to avoid movement
333 asm volatile("__cfaasm_enble_after:":::"memory");
334 }
335
336 // Disable interrupts by incrementint the counter
337 // Don't execute any pending __cfactx_switch even if counter reaches 0
338 void enable_interrupts_noPoll() {
339 // create a assembler label before
340 // marked as clobber all to avoid movement
341 asm volatile("__cfaasm_nopoll_before:":::"memory");
342
343 unsigned short prev = __cfaabi_tls.preemption_state.disable_count;
344 __cfaabi_tls.preemption_state.disable_count -= 1;
345 verifyf( prev != 0u, "Incremented from %u\n", prev ); // If this triggers someone is enabled already enabled interrupts
346 if( prev == 1 ) {
347 #if GCC_VERSION > 50000
348 static_assert(__atomic_always_lock_free(sizeof(__cfaabi_tls.preemption_state.enabled), &__cfaabi_tls.preemption_state.enabled), "Must be lock-free");
349 #endif
350 // Set enabled flag to true
351 // should be atomic to avoid preemption in the middle of the operation.
352 // use memory order RELAXED since there is no inter-thread on this variable requirements
353 __atomic_store_n(&__cfaabi_tls.preemption_state.enabled, true, __ATOMIC_RELAXED);
354
355 // Signal the compiler that a fence is needed but only for signal handlers
356 __atomic_signal_fence(__ATOMIC_RELEASE);
357 }
358
359 // create a assembler label after
360 // marked as clobber all to avoid movement
361 asm volatile("__cfaasm_nopoll_after:":::"memory");
362 }
363}
364
365// sigprocmask wrapper : unblock a single signal
366static inline void signal_unblock( int sig ) {
367 sigset_t mask;
368 sigemptyset( &mask );
369 sigaddset( &mask, sig );
370
371 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
372 abort( "internal error, pthread_sigmask" );
373 }
374}
375
376// sigprocmask wrapper : block a single signal
377static inline void signal_block( int sig ) {
378 sigset_t mask;
379 sigemptyset( &mask );
380 sigaddset( &mask, sig );
381
382 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
383 abort( "internal error, pthread_sigmask" );
384 }
385}
386
387// kill wrapper : signal a processor
388static void preempt( processor * this ) {
389 sigval_t value = { PREEMPT_NORMAL };
390 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
391}
392
393// reserved for future use
394static void timeout( $thread * this ) {
395 #if !defined( __CFA_NO_STATISTICS__ )
396 kernelTLS().this_stats = this->curr_cluster->stats;
397 #endif
398 unpark( this );
399}
400
401//-----------------------------------------------------------------------------
402// Some assembly required
403#if defined( __i386 )
404 #ifdef __PIC__
405 #define RELOC_PRELUDE( label ) \
406 "calll .Lcfaasm_prelude_" #label "$pb\n\t" \
407 ".Lcfaasm_prelude_" #label "$pb:\n\t" \
408 "popl %%eax\n\t" \
409 ".Lcfaasm_prelude_" #label "_end:\n\t" \
410 "addl $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
411 #define RELOC_PREFIX ""
412 #define RELOC_SUFFIX "@GOT(%%eax)"
413 #else
414 #define RELOC_PREFIX "$"
415 #define RELOC_SUFFIX ""
416 #endif
417 #define __cfaasm_label( label ) static struct asm_region label = \
418 ({ \
419 struct asm_region region; \
420 asm( \
421 RELOC_PRELUDE( label ) \
422 "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
423 "movl " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
424 : [vb]"=r"(region.before), [va]"=r"(region.after) \
425 ); \
426 region; \
427 });
428#elif defined( __x86_64 )
429 #ifdef __PIC__
430 #define RELOC_PREFIX ""
431 #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
432 #else
433 #define RELOC_PREFIX "$"
434 #define RELOC_SUFFIX ""
435 #endif
436 #define __cfaasm_label( label ) static struct asm_region label = \
437 ({ \
438 struct asm_region region; \
439 asm( \
440 "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
441 "movq " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
442 : [vb]"=r"(region.before), [va]"=r"(region.after) \
443 ); \
444 region; \
445 });
446#elif defined( __aarch64__ )
447 #ifdef __PIC__
448 #define RELOC_TAG "@PLT"
449 #else
450 #define RELOC_TAG ""
451 #endif
452 #define __cfaasm_label( label ) \
453 ({ \
454 struct asm_region region; \
455 asm( \
456 "mov %[vb], __cfaasm_" #label "_before@GOTPCREL(%%rip)" "\n\t" \
457 "mov %[va], __cfaasm_" #label "_after@GOTPCREL(%%rip)" "\n\t" \
458 : [vb]"=r"(region.before), [va]"=r"(region.after) \
459 ); \
460 region; \
461 });
462#else
463 #error unknown hardware architecture
464#endif
465
466// KERNEL ONLY
467// Check if a __cfactx_switch signal handler shoud defer
468// If true : preemption is safe
469// If false : preemption is unsafe and marked as pending
470static inline bool preemption_ready( void * ip ) {
471 // Get all the region for which it is not safe to preempt
472 __cfaasm_label( get );
473 __cfaasm_label( check );
474 __cfaasm_label( dsable );
475 __cfaasm_label( enble );
476 __cfaasm_label( nopoll );
477
478 // Check if preemption is safe
479 bool ready = true;
480 if( __cfaasm_in( ip, get ) ) { ready = false; goto EXIT; };
481 if( __cfaasm_in( ip, check ) ) { ready = false; goto EXIT; };
482 if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
483 if( __cfaasm_in( ip, enble ) ) { ready = false; goto EXIT; };
484 if( __cfaasm_in( ip, nopoll ) ) { ready = false; goto EXIT; };
485 if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
486 if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
487
488EXIT:
489 // Adjust the pending flag accordingly
490 __cfaabi_tls.this_processor->pending_preemption = !ready;
491 return ready;
492}
493
494//=============================================================================================
495// Kernel Signal Startup/Shutdown logic
496//=============================================================================================
497
498// Startup routine to activate preemption
499// Called from kernel_startup
500void __kernel_alarm_startup() {
501 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
502
503 // Start with preemption disabled until ready
504 __cfaabi_tls.preemption_state.enabled = false;
505 __cfaabi_tls.preemption_state.disable_count = 1;
506
507 // Initialize the event kernel
508 event_kernel = (event_kernel_t *)&storage_event_kernel;
509 (*event_kernel){};
510
511 // Setup proper signal handlers
512 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
513 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO | SA_RESTART ); // debug handler
514
515 signal_block( SIGALRM );
516
517 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
518}
519
520// Shutdown routine to deactivate preemption
521// Called from kernel_shutdown
522void __kernel_alarm_shutdown() {
523 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
524
525 // Block all signals since we are already shutting down
526 sigset_t mask;
527 sigfillset( &mask );
528 sigprocmask( SIG_BLOCK, &mask, 0p );
529
530 // Notify the alarm thread of the shutdown
531 sigval val = { 1 };
532 pthread_sigqueue( alarm_thread, SIGALRM, val );
533
534 // Wait for the preemption thread to finish
535
536 pthread_join( alarm_thread, 0p );
537 free( alarm_stack );
538
539 // Preemption is now fully stopped
540
541 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
542}
543
544// Raii ctor/dtor for the preemption_scope
545// Used by thread to control when they want to receive preemption signals
546void ?{}( preemption_scope & this, processor * proc ) {
547 (this.alarm){ proc, (Time){ 0 }, 0`s };
548 this.proc = proc;
549 this.proc->preemption_alarm = &this.alarm;
550
551 update_preemption( this.proc, this.proc->cltr->preemption_rate );
552}
553
554void ^?{}( preemption_scope & this ) {
555 disable_interrupts();
556
557 update_preemption( this.proc, 0`s );
558}
559
560//=============================================================================================
561// Kernel Signal Handlers
562//=============================================================================================
563__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
564
565// Context switch signal handler
566// Receives SIGUSR1 signal and causes the current thread to yield
567static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
568 void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
569 __cfaabi_dbg_debug_do( last_interrupt = ip; )
570
571 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
572 // the interrupt that is supposed to force the kernel thread to preempt might arrive
573 // before the kernel thread has even started running. When that happens, an interrupt
574 // with a null 'this_processor' will be caught, just ignore it.
575 if(! __cfaabi_tls.this_processor ) return;
576
577 choose(sfp->si_value.sival_int) {
578 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
579 case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
580 default:
581 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
582 }
583
584 // Check if it is safe to preempt here
585 if( !preemption_ready( ip ) ) { return; }
586
587 __cfaabi_dbg_print_buffer_decl( " KERNEL: preempting core %p (%p @ %p).\n", __cfaabi_tls.this_processor, __cfaabi_tls.this_thread, (void *)(cxt->uc_mcontext.CFA_REG_IP) );
588
589 // Sync flag : prevent recursive calls to the signal handler
590 __cfaabi_tls.preemption_state.in_progress = true;
591
592 // Clear sighandler mask before context switching.
593 #if GCC_VERSION > 50000
594 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
595 #endif
596 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
597 abort( "internal error, sigprocmask" );
598 }
599
600 // Clear the in progress flag
601 __cfaabi_tls.preemption_state.in_progress = false;
602
603 // Preemption can occur here
604
605 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
606}
607
608static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
609 abort("SIGALRM should never reach the signal handler");
610}
611
612// Main of the alarm thread
613// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
614static void * alarm_loop( __attribute__((unused)) void * args ) {
615 __processor_id_t id;
616 id.full_proc = false;
617 id.id = doregister(&id);
618 __cfaabi_tls.this_proc_id = &id;
619
620 // Block sigalrms to control when they arrive
621 sigset_t mask;
622 sigfillset(&mask);
623 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
624 abort( "internal error, pthread_sigmask" );
625 }
626
627 sigemptyset( &mask );
628 sigaddset( &mask, SIGALRM );
629
630 // Main loop
631 while( true ) {
632 // Wait for a sigalrm
633 siginfo_t info;
634 int sig = sigwaitinfo( &mask, &info );
635
636 if( sig < 0 ) {
637 //Error!
638 int err = errno;
639 switch( err ) {
640 case EAGAIN :
641 case EINTR :
642 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
643 continue;
644 case EINVAL :
645 abort( "Timeout was invalid." );
646 default:
647 abort( "Unhandled error %d", err);
648 }
649 }
650
651 // If another signal arrived something went wrong
652 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
653
654 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
655 // Switch on the code (a.k.a. the sender) to
656 switch( info.si_code )
657 {
658 // Timers can apparently be marked as sent for the kernel
659 // In either case, tick preemption
660 case SI_TIMER:
661 case SI_KERNEL:
662 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
663 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
664 tick_preemption();
665 unlock( event_kernel->lock );
666 break;
667 // Signal was not sent by the kernel but by an other thread
668 case SI_QUEUE:
669 // For now, other thread only signal the alarm thread to shut it down
670 // If this needs to change use info.si_value and handle the case here
671 goto EXIT;
672 }
673 }
674
675EXIT:
676 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
677 unregister(&id);
678 return 0p;
679}
680
681//=============================================================================================
682// Kernel Signal Debug
683//=============================================================================================
684
685void __cfaabi_check_preemption() {
686 bool ready = __preemption_enabled();
687 if(!ready) { abort("Preemption should be ready"); }
688
689 sigset_t oldset;
690 int ret;
691 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
692 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
693
694 ret = sigismember(&oldset, SIGUSR1);
695 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
696 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
697
698 ret = sigismember(&oldset, SIGALRM);
699 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
700 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
701
702 ret = sigismember(&oldset, SIGTERM);
703 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
704 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
705}
706
707#ifdef __CFA_WITH_VERIFY__
708bool __cfaabi_dbg_in_kernel() {
709 return !__preemption_enabled();
710}
711#endif
712
713// Local Variables: //
714// mode: c //
715// tab-width: 4 //
716// End: //
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