source: libcfa/src/concurrency/preemption.cfa@ ad4832f1

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 ad4832f1 was ead174a, checked in by Thierry Delisle <tdelisle@…>, 5 years ago

Fixed implementation of TLS protection for aarch64
  • 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// Some assembly required
219#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
220
221//----------
222// special case for preemption since used often
223bool __preemption_enabled() {
224 // create a assembler label before
225 // marked as clobber all to avoid movement
226 __cfaasm_label(check, before);
227
228 // access tls as normal
229 bool enabled = __cfaabi_tls.preemption_state.enabled;
230
231 // create a assembler label after
232 // marked as clobber all to avoid movement
233 __cfaasm_label(check, after);
234 return enabled;
235}
236
237struct asm_region {
238 void * before;
239 void * after;
240};
241
242static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
243 return ip >= region.before && ip <= region.after;
244}
245
246
247//----------
248// Get data from the TLS block
249// struct asm_region __cfaasm_get;
250uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
251uintptr_t __cfatls_get( unsigned long int offset ) {
252 // create a assembler label before
253 // marked as clobber all to avoid movement
254 __cfaasm_label(get, before);
255
256 // access tls as normal (except for pointer arithmetic)
257 uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
258
259 // create a assembler label after
260 // marked as clobber all to avoid movement
261 __cfaasm_label(get, after);
262 return val;
263}
264
265extern "C" {
266 // Disable interrupts by incrementing the counter
267 void disable_interrupts() {
268 // create a assembler label before
269 // marked as clobber all to avoid movement
270 __cfaasm_label(dsable, before);
271
272 with( __cfaabi_tls.preemption_state ) {
273 #if GCC_VERSION > 50000
274 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
275 #endif
276
277 // Set enabled flag to false
278 // should be atomic to avoid preemption in the middle of the operation.
279 // use memory order RELAXED since there is no inter-thread on this variable requirements
280 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
281
282 // Signal the compiler that a fence is needed but only for signal handlers
283 __atomic_signal_fence(__ATOMIC_ACQUIRE);
284
285 __attribute__((unused)) unsigned short new_val = disable_count + 1;
286 disable_count = new_val;
287 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
288 }
289
290 // create a assembler label after
291 // marked as clobber all to avoid movement
292 __cfaasm_label(dsable, after);
293
294 }
295
296 // Enable interrupts by decrementing the counter
297 // If counter reaches 0, execute any pending __cfactx_switch
298 void enable_interrupts( __cfaabi_dbg_ctx_param ) {
299 // Cache the processor now since interrupts can start happening after the atomic store
300 processor * proc = __cfaabi_tls.this_processor;
301 /* paranoid */ verify( proc );
302
303 with( __cfaabi_tls.preemption_state ){
304 unsigned short prev = disable_count;
305 disable_count -= 1;
306
307 // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
308 /* paranoid */ verify( prev != 0u );
309
310 // Check if we need to prempt the thread because an interrupt was missed
311 if( prev == 1 ) {
312 #if GCC_VERSION > 50000
313 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
314 #endif
315
316 // Set enabled flag to true
317 // should be atomic to avoid preemption in the middle of the operation.
318 // use memory order RELAXED since there is no inter-thread on this variable requirements
319 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
320
321 // Signal the compiler that a fence is needed but only for signal handlers
322 __atomic_signal_fence(__ATOMIC_RELEASE);
323 if( proc->pending_preemption ) {
324 proc->pending_preemption = false;
325 force_yield( __POLL_PREEMPTION );
326 }
327 }
328 }
329
330 // For debugging purposes : keep track of the last person to enable the interrupts
331 __cfaabi_dbg_debug_do( proc->last_enable = caller; )
332 }
333
334 // Disable interrupts by incrementint the counter
335 // Don't execute any pending __cfactx_switch even if counter reaches 0
336 void enable_interrupts_noPoll() {
337 unsigned short prev = __cfaabi_tls.preemption_state.disable_count;
338 __cfaabi_tls.preemption_state.disable_count -= 1;
339 // If this triggers someone is enabled already enabled interrupts
340 /* paranoid */ verifyf( prev != 0u, "Incremented from %u\n", prev );
341 if( prev == 1 ) {
342 #if GCC_VERSION > 50000
343 static_assert(__atomic_always_lock_free(sizeof(__cfaabi_tls.preemption_state.enabled), &__cfaabi_tls.preemption_state.enabled), "Must be lock-free");
344 #endif
345 // Set enabled flag to true
346 // should be atomic to avoid preemption in the middle of the operation.
347 // use memory order RELAXED since there is no inter-thread on this variable requirements
348 __atomic_store_n(&__cfaabi_tls.preemption_state.enabled, true, __ATOMIC_RELAXED);
349
350 // Signal the compiler that a fence is needed but only for signal handlers
351 __atomic_signal_fence(__ATOMIC_RELEASE);
352 }
353 }
354}
355
356#undef __cfaasm_label
357
358// sigprocmask wrapper : unblock a single signal
359static inline void signal_unblock( int sig ) {
360 sigset_t mask;
361 sigemptyset( &mask );
362 sigaddset( &mask, sig );
363
364 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
365 abort( "internal error, pthread_sigmask" );
366 }
367}
368
369// sigprocmask wrapper : block a single signal
370static inline void signal_block( int sig ) {
371 sigset_t mask;
372 sigemptyset( &mask );
373 sigaddset( &mask, sig );
374
375 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
376 abort( "internal error, pthread_sigmask" );
377 }
378}
379
380// kill wrapper : signal a processor
381static void preempt( processor * this ) {
382 sigval_t value = { PREEMPT_NORMAL };
383 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
384}
385
386// reserved for future use
387static void timeout( $thread * this ) {
388 #if !defined( __CFA_NO_STATISTICS__ )
389 kernelTLS().this_stats = this->curr_cluster->stats;
390 #endif
391 unpark( this );
392}
393
394//-----------------------------------------------------------------------------
395// Some assembly required
396#if defined( __i386 )
397 #ifdef __PIC__
398 #define RELOC_PRELUDE( label ) \
399 "calll .Lcfaasm_prelude_" #label "$pb\n\t" \
400 ".Lcfaasm_prelude_" #label "$pb:\n\t" \
401 "popl %%eax\n\t" \
402 ".Lcfaasm_prelude_" #label "_end:\n\t" \
403 "addl $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
404 #define RELOC_PREFIX ""
405 #define RELOC_SUFFIX "@GOT(%%eax)"
406 #else
407 #define RELOC_PREFIX "$"
408 #define RELOC_SUFFIX ""
409 #endif
410 #define __cfaasm_label( label ) static struct asm_region label = \
411 ({ \
412 struct asm_region region; \
413 asm( \
414 RELOC_PRELUDE( label ) \
415 "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
416 "movl " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
417 : [vb]"=r"(region.before), [va]"=r"(region.after) \
418 ); \
419 region; \
420 });
421#elif defined( __x86_64 )
422 #ifdef __PIC__
423 #define RELOC_PREFIX ""
424 #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
425 #else
426 #define RELOC_PREFIX "$"
427 #define RELOC_SUFFIX ""
428 #endif
429 #define __cfaasm_label( label ) static struct asm_region label = \
430 ({ \
431 struct asm_region region; \
432 asm( \
433 "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
434 "movq " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
435 : [vb]"=r"(region.before), [va]"=r"(region.after) \
436 ); \
437 region; \
438 });
439#elif defined( __aarch64__ )
440 #ifdef __PIC__
441 // Note that this works only for gcc
442 #define __cfaasm_label( label ) static struct asm_region label = \
443 ({ \
444 struct asm_region region; \
445 asm( \
446 "adrp %[vb], _GLOBAL_OFFSET_TABLE_" "\n\t" \
447 "ldr %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
448 "adrp %[va], _GLOBAL_OFFSET_TABLE_" "\n\t" \
449 "ldr %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]" "\n\t" \
450 : [vb]"=r"(region.before), [va]"=r"(region.after) \
451 ); \
452 region; \
453 });
454 #else
455 #error this is not the right thing to do
456 // #define __cfaasm_label( label ) static struct asm_region label = \
457 // ({ \
458 // struct asm_region region; \
459 // asm( \
460 // "adrp %[vb], __cfaasm_" #label "_before" "\n\t" \
461 // "add %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
462 // "adrp %[va], :got:__cfaasm_" #label "_after" "\n\t" \
463 // "add %[va], %[va], :lo12:__cfaasm_" #label "_after" "\n\t" \
464 // : [vb]"=r"(region.before), [va]"=r"(region.after) \
465 // ); \
466 // region; \
467 // });
468 #endif
469#else
470 #error unknown hardware architecture
471#endif
472
473// KERNEL ONLY
474// Check if a __cfactx_switch signal handler shoud defer
475// If true : preemption is safe
476// If false : preemption is unsafe and marked as pending
477static inline bool preemption_ready( void * ip ) {
478 // Get all the region for which it is not safe to preempt
479 __cfaasm_label( get );
480 __cfaasm_label( check );
481 __cfaasm_label( dsable );
482
483 // Check if preemption is safe
484 bool ready = true;
485 if( __cfaasm_in( ip, get ) ) { ready = false; goto EXIT; };
486 if( __cfaasm_in( ip, check ) ) { ready = false; goto EXIT; };
487 if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
488 if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
489 if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
490
491EXIT:
492 // Adjust the pending flag accordingly
493 __cfaabi_tls.this_processor->pending_preemption = !ready;
494 return ready;
495}
496
497//=============================================================================================
498// Kernel Signal Startup/Shutdown logic
499//=============================================================================================
500
501// Startup routine to activate preemption
502// Called from kernel_startup
503void __kernel_alarm_startup() {
504 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
505
506 // Start with preemption disabled until ready
507 __cfaabi_tls.preemption_state.enabled = false;
508 __cfaabi_tls.preemption_state.disable_count = 1;
509
510 // Initialize the event kernel
511 event_kernel = (event_kernel_t *)&storage_event_kernel;
512 (*event_kernel){};
513
514 // Setup proper signal handlers
515 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO | SA_RESTART ); // __cfactx_switch handler
516 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO | SA_RESTART ); // debug handler
517
518 signal_block( SIGALRM );
519
520 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
521}
522
523// Shutdown routine to deactivate preemption
524// Called from kernel_shutdown
525void __kernel_alarm_shutdown() {
526 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
527
528 // Block all signals since we are already shutting down
529 sigset_t mask;
530 sigfillset( &mask );
531 sigprocmask( SIG_BLOCK, &mask, 0p );
532
533 // Notify the alarm thread of the shutdown
534 sigval val = { 1 };
535 pthread_sigqueue( alarm_thread, SIGALRM, val );
536
537 // Wait for the preemption thread to finish
538
539 pthread_join( alarm_thread, 0p );
540 free( alarm_stack );
541
542 // Preemption is now fully stopped
543
544 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
545}
546
547// Raii ctor/dtor for the preemption_scope
548// Used by thread to control when they want to receive preemption signals
549void ?{}( preemption_scope & this, processor * proc ) {
550 (this.alarm){ proc, (Time){ 0 }, 0`s };
551 this.proc = proc;
552 this.proc->preemption_alarm = &this.alarm;
553
554 update_preemption( this.proc, this.proc->cltr->preemption_rate );
555}
556
557void ^?{}( preemption_scope & this ) {
558 disable_interrupts();
559
560 update_preemption( this.proc, 0`s );
561}
562
563//=============================================================================================
564// Kernel Signal Handlers
565//=============================================================================================
566__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
567
568// Context switch signal handler
569// Receives SIGUSR1 signal and causes the current thread to yield
570static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
571 void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
572 __cfaabi_dbg_debug_do( last_interrupt = ip; )
573
574 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
575 // the interrupt that is supposed to force the kernel thread to preempt might arrive
576 // before the kernel thread has even started running. When that happens, an interrupt
577 // with a null 'this_processor' will be caught, just ignore it.
578 if(! __cfaabi_tls.this_processor ) return;
579
580 choose(sfp->si_value.sival_int) {
581 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
582 case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
583 default:
584 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
585 }
586
587 // Check if it is safe to preempt here
588 if( !preemption_ready( ip ) ) { return; }
589
590 __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) );
591
592 // Sync flag : prevent recursive calls to the signal handler
593 __cfaabi_tls.preemption_state.in_progress = true;
594
595 // Clear sighandler mask before context switching.
596 #if GCC_VERSION > 50000
597 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
598 #endif
599 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
600 abort( "internal error, sigprocmask" );
601 }
602
603 // Clear the in progress flag
604 __cfaabi_tls.preemption_state.in_progress = false;
605
606 // Preemption can occur here
607
608 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
609}
610
611static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
612 abort("SIGALRM should never reach the signal handler");
613}
614
615// Main of the alarm thread
616// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
617static void * alarm_loop( __attribute__((unused)) void * args ) {
618 __processor_id_t id;
619 id.full_proc = false;
620 id.id = doregister(&id);
621 __cfaabi_tls.this_proc_id = &id;
622
623 // Block sigalrms to control when they arrive
624 sigset_t mask;
625 sigfillset(&mask);
626 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
627 abort( "internal error, pthread_sigmask" );
628 }
629
630 sigemptyset( &mask );
631 sigaddset( &mask, SIGALRM );
632
633 // Main loop
634 while( true ) {
635 // Wait for a sigalrm
636 siginfo_t info;
637 int sig = sigwaitinfo( &mask, &info );
638
639 if( sig < 0 ) {
640 //Error!
641 int err = errno;
642 switch( err ) {
643 case EAGAIN :
644 case EINTR :
645 {__cfaabi_dbg_print_buffer_decl( " KERNEL: Spurious wakeup %d.\n", err );}
646 continue;
647 case EINVAL :
648 abort( "Timeout was invalid." );
649 default:
650 abort( "Unhandled error %d", err);
651 }
652 }
653
654 // If another signal arrived something went wrong
655 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
656
657 // __cfaabi_dbg_print_safe( "Kernel : Caught alarm from %d with %d\n", info.si_code, info.si_value.sival_int );
658 // Switch on the code (a.k.a. the sender) to
659 switch( info.si_code )
660 {
661 // Timers can apparently be marked as sent for the kernel
662 // In either case, tick preemption
663 case SI_TIMER:
664 case SI_KERNEL:
665 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
666 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
667 tick_preemption();
668 unlock( event_kernel->lock );
669 break;
670 // Signal was not sent by the kernel but by an other thread
671 case SI_QUEUE:
672 // For now, other thread only signal the alarm thread to shut it down
673 // If this needs to change use info.si_value and handle the case here
674 goto EXIT;
675 }
676 }
677
678EXIT:
679 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
680 unregister(&id);
681 return 0p;
682}
683
684//=============================================================================================
685// Kernel Signal Debug
686//=============================================================================================
687
688void __cfaabi_check_preemption() {
689 bool ready = __preemption_enabled();
690 if(!ready) { abort("Preemption should be ready"); }
691
692 sigset_t oldset;
693 int ret;
694 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
695 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
696
697 ret = sigismember(&oldset, SIGUSR1);
698 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
699 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
700
701 ret = sigismember(&oldset, SIGALRM);
702 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
703 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
704
705 ret = sigismember(&oldset, SIGTERM);
706 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
707 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
708}
709
710#ifdef __CFA_WITH_VERIFY__
711bool __cfaabi_dbg_in_kernel() {
712 return !__preemption_enabled();
713}
714#endif
715
716// Local Variables: //
717// mode: c //
718// tab-width: 4 //
719// End: //
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