source: libcfa/src/concurrency/preemption.cfa@ b56ad5e

ADT ast-experimental enum forall-pointer-decay pthread-emulation qualifiedEnum
Last change on this file since b56ad5e was becb85b9, checked in by Thierry Delisle <tdelisle@…>, 4 years ago

Attempt to fix preemption deadlock.
No longer prevent preemption during cfaabi_check_preemption.
preemption_enabled() now does a roll forward if it blocked a preemption.
  • Property mode set to 100644
File size: 26.5 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#define _GNU_SOURCE
18
19// #define __CFA_DEBUG_PRINT_PREEMPTION__
20
21#include "preemption.hfa"
22
23#include <assert.h>
24
25#include <errno.h>
26#include <stdio.h>
27#include <string.h>
28#include <unistd.h>
29#include <limits.h> // PTHREAD_STACK_MIN
30
31#include "bits/debug.hfa"
32#include "bits/signal.hfa"
33#include "kernel_private.hfa"
34
35
36#if !defined(__CFA_DEFAULT_PREEMPTION__)
37#define __CFA_DEFAULT_PREEMPTION__ 10`ms
38#endif
39
40__attribute__((weak)) Duration default_preemption() {
41 const char * preempt_rate_s = getenv("CFA_DEFAULT_PREEMPTION");
42 if(!preempt_rate_s) {
43 __cfadbg_print_safe(preemption, "No CFA_DEFAULT_PREEMPTION in ENV\n");
44 return __CFA_DEFAULT_PREEMPTION__;
45 }
46
47 char * endptr = 0p;
48 long int preempt_rate_l = strtol(preempt_rate_s, &endptr, 10);
49 if(preempt_rate_l < 0 || preempt_rate_l > 65535) {
50 __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION out of range : %ld\n", preempt_rate_l);
51 return __CFA_DEFAULT_PREEMPTION__;
52 }
53 if('\0' != *endptr) {
54 __cfadbg_print_safe(preemption, "CFA_DEFAULT_PREEMPTION not a decimal number : %s\n", preempt_rate_s);
55 return __CFA_DEFAULT_PREEMPTION__;
56 }
57
58 return preempt_rate_l`ms;
59}
60
61// FwdDeclarations : timeout handlers
62static void preempt( processor * this );
63static void timeout( thread$ * this );
64
65// FwdDeclarations : Signal handlers
66static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ );
67static void sigHandler_alarm ( __CFA_SIGPARMS__ );
68static void sigHandler_segv ( __CFA_SIGPARMS__ );
69static void sigHandler_ill ( __CFA_SIGPARMS__ );
70static void sigHandler_fpe ( __CFA_SIGPARMS__ );
71static void sigHandler_abort ( __CFA_SIGPARMS__ );
72
73// FwdDeclarations : alarm thread main
74static void * alarm_loop( __attribute__((unused)) void * args );
75
76// Machine specific register name
77#if defined( __i386 )
78#define CFA_REG_IP gregs[REG_EIP]
79#elif defined( __x86_64 )
80#define CFA_REG_IP gregs[REG_RIP]
81#elif defined( __arm__ )
82#define CFA_REG_IP arm_pc
83#elif defined( __aarch64__ )
84#define CFA_REG_IP pc
85#else
86#error unsupported hardware architecture
87#endif
88
89KERNEL_STORAGE(event_kernel_t, event_kernel); // private storage for event kernel
90event_kernel_t * event_kernel; // kernel public handle to even kernel
91static pthread_t alarm_thread; // pthread handle to alarm thread
92static void * alarm_stack; // pthread stack for alarm thread
93
94static void ?{}(event_kernel_t & this) with( this ) {
95 alarms{};
96 lock{};
97}
98
99enum {
100 PREEMPT_NORMAL = 0,
101 PREEMPT_TERMINATE = 1,
102};
103
104//=============================================================================================
105// Kernel Preemption logic
106//=============================================================================================
107
108// Get next expired node
109static inline alarm_node_t * get_expired( alarm_list_t * alarms, Time currtime ) {
110 if( ! & (*alarms)`first ) return 0p; // If no alarms return null
111 if( (*alarms)`first.timeval >= currtime ) return 0p; // If alarms head not expired return null
112 return pop(alarms); // Otherwise just pop head
113}
114
115// Tick one frame of the Discrete Event Simulation for alarms
116static void tick_preemption(void) {
117 alarm_node_t * node = 0p; // Used in the while loop but cannot be declared in the while condition
118 alarm_list_t * alarms = &event_kernel->alarms; // Local copy for ease of reading
119 Time currtime = __kernel_get_time(); // Check current time once so everything "happens at once"
120
121 //Loop throught every thing expired
122 while( node = get_expired( alarms, currtime ) ) {
123 __cfadbg_print_buffer_decl( preemption, " KERNEL: preemption tick %lu\n", currtime.tn);
124 Duration period = node->period;
125 if( period == 0) {
126 node->set = false; // Node is one-shot, just mark it as not pending
127 }
128
129 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm ticking node %p.\n", node );
130
131
132 // Check if this is a kernel
133 if( node->type == Kernel ) {
134 preempt( node->proc );
135 }
136 else if( node->type == User ) {
137 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm unparking %p.\n", node->thrd );
138 timeout( node->thrd );
139 }
140 else {
141 node->callback(*node);
142 }
143
144 // Check if this is a periodic alarm
145 if( period > 0 ) {
146 __cfadbg_print_buffer_local( preemption, " KERNEL: alarm period is %lu.\n", period`ns );
147 node->timeval = currtime + period; // Alarm is periodic, add currtime to it (used cached current time)
148 insert( alarms, node ); // Reinsert the node for the next time it triggers
149 }
150 }
151
152 // If there are still alarms pending, reset the timer
153 if( & (*alarms)`first ) {
154 Duration delta = (*alarms)`first.timeval - currtime;
155 __kernel_set_timer( delta );
156 }
157}
158
159// Update the preemption of a processor and notify interested parties
160void update_preemption( processor * this, Duration duration ) {
161 alarm_node_t * alarm = this->preemption_alarm;
162
163 // Alarms need to be enabled
164 if ( duration > 0 && ! alarm->set ) {
165 alarm->initial = duration;
166 alarm->period = duration;
167 register_self( alarm );
168 }
169 // Zero duration but alarm is set
170 else if ( duration == 0 && alarm->set ) {
171 unregister_self( alarm );
172 alarm->initial = 0;
173 alarm->period = 0;
174 }
175 // If alarm is different from previous, change it
176 else if ( duration > 0 && alarm->period != duration ) {
177 unregister_self( alarm );
178 alarm->initial = duration;
179 alarm->period = duration;
180 register_self( alarm );
181 }
182}
183
184//=============================================================================================
185// Kernel Signal Tools
186//=============================================================================================
187// In a user-level threading system, there are handful of thread-local variables where this problem occurs on the ARM.
188//
189// For each kernel thread running user-level threads, there is a flag variable to indicate if interrupts are
190// enabled/disabled for that kernel thread. Therefore, this variable is made thread local.
191//
192// For example, this code fragment sets the state of the "interrupt" variable in thread-local memory.
193//
194// _Thread_local volatile int interrupts;
195// int main() {
196// interrupts = 0; // disable interrupts }
197//
198// which generates the following code on the ARM
199//
200// (gdb) disassemble main
201// Dump of assembler code for function main:
202// 0x0000000000000610 <+0>: mrs x1, tpidr_el0
203// 0x0000000000000614 <+4>: mov w0, #0x0 // #0
204// 0x0000000000000618 <+8>: add x1, x1, #0x0, lsl #12
205// 0x000000000000061c <+12>: add x1, x1, #0x10
206// 0x0000000000000620 <+16>: str wzr, [x1]
207// 0x0000000000000624 <+20>: ret
208//
209// The mrs moves a pointer from coprocessor register tpidr_el0 into register x1. Register w0 is set to 0. The two adds
210// increase the TLS pointer with the displacement (offset) 0x10, which is the location in the TSL of variable
211// "interrupts". Finally, 0 is stored into "interrupts" through the pointer in register x1 that points into the
212// TSL. Now once x1 has the pointer to the location of the TSL for kernel thread N, it can be be preempted at a
213// user-level and the user thread is put on the user-level ready-queue. When the preempted thread gets to the front of
214// the user-level ready-queue it is run on kernel thread M. It now stores 0 into "interrupts" back on kernel thread N,
215// turning off interrupt on the wrong kernel thread.
216//
217// On the x86, the following code is generated for the same code fragment.
218//
219// (gdb) disassemble main
220// Dump of assembler code for function main:
221// 0x0000000000400420 <+0>: movl $0x0,%fs:0xfffffffffffffffc
222// 0x000000000040042c <+12>: xor %eax,%eax
223// 0x000000000040042e <+14>: retq
224//
225// and there is base-displacement addressing used to atomically reset variable "interrupts" off of the TSL pointer in
226// register "fs".
227//
228// Hence, the ARM has base-displacement address for the general purpose registers, BUT not to the coprocessor
229// registers. As a result, generating the address for the write into variable "interrupts" is no longer atomic.
230//
231// Note this problem does NOT occur when just using multiple kernel threads because the preemption ALWAYS restarts the
232// thread on the same kernel thread.
233//
234// The obvious question is why does ARM use a coprocessor register to store the TSL pointer given that coprocessor
235// registers are second-class registers with respect to the instruction set. One possible answer is that they did not
236// want to dedicate one of the general registers to hold the TLS pointer and there was a free coprocessor register
237// available.
238
239//-----------------------------------------------------------------------------
240// Some assembly required
241#define __cfaasm_label(label, when) when: asm volatile goto(".global __cfaasm_" #label "_" #when "\n" "__cfaasm_" #label "_" #when ":":::"memory":when)
242
243//----------
244// special case for preemption since used often
245bool __preemption_enabled() {
246 // create a assembler label before
247 // marked as clobber all to avoid movement
248 __cfaasm_label(check, before);
249
250 // access tls as normal
251 bool enabled = __cfaabi_tls.preemption_state.enabled;
252
253 // Check if there is a pending preemption
254 processor * proc = __cfaabi_tls.this_processor;
255 bool pending = proc ? proc->pending_preemption : false;
256 if( enabled && pending ) proc->pending_preemption = false;
257
258 // create a assembler label after
259 // marked as clobber all to avoid movement
260 __cfaasm_label(check, after);
261
262 // If we can preempt and there is a pending one
263 // this is a good time to yield
264 if( enabled && pending ) {
265 force_yield( __POLL_PREEMPTION );
266 }
267 return enabled;
268}
269
270struct asm_region {
271 void * before;
272 void * after;
273};
274
275static inline bool __cfaasm_in( void * ip, struct asm_region & region ) {
276 return ip >= region.before && ip <= region.after;
277}
278
279
280//----------
281// Get data from the TLS block
282// struct asm_region __cfaasm_get;
283uintptr_t __cfatls_get( unsigned long int offset ) __attribute__((__noinline__)); //no inline to avoid problems
284uintptr_t __cfatls_get( unsigned long int offset ) {
285 // create a assembler label before
286 // marked as clobber all to avoid movement
287 __cfaasm_label(get, before);
288
289 // access tls as normal (except for pointer arithmetic)
290 uintptr_t val = *(uintptr_t*)((uintptr_t)&__cfaabi_tls + offset);
291
292 // create a assembler label after
293 // marked as clobber all to avoid movement
294 __cfaasm_label(get, after);
295
296 // This is used everywhere, to avoid cost, we DO NOT poll pending preemption
297 return val;
298}
299
300extern "C" {
301 // Disable interrupts by incrementing the counter
302 void disable_interrupts() {
303 // create a assembler label before
304 // marked as clobber all to avoid movement
305 __cfaasm_label(dsable, before);
306
307 with( __cfaabi_tls.preemption_state ) {
308 #if GCC_VERSION > 50000
309 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
310 #endif
311
312 // Set enabled flag to false
313 // should be atomic to avoid preemption in the middle of the operation.
314 // use memory order RELAXED since there is no inter-thread on this variable requirements
315 __atomic_store_n(&enabled, false, __ATOMIC_RELAXED);
316
317 // Signal the compiler that a fence is needed but only for signal handlers
318 __atomic_signal_fence(__ATOMIC_ACQUIRE);
319
320 __attribute__((unused)) unsigned short new_val = disable_count + 1;
321 disable_count = new_val;
322 verify( new_val < 65_000u ); // If this triggers someone is disabling interrupts without enabling them
323 }
324
325 // create a assembler label after
326 // marked as clobber all to avoid movement
327 __cfaasm_label(dsable, after);
328
329 }
330
331 // Enable interrupts by decrementing the counter
332 // If counter reaches 0, execute any pending __cfactx_switch
333 void enable_interrupts( bool poll ) {
334 // Cache the processor now since interrupts can start happening after the atomic store
335 processor * proc = __cfaabi_tls.this_processor;
336 /* paranoid */ verify( !poll || proc );
337
338 with( __cfaabi_tls.preemption_state ){
339 unsigned short prev = disable_count;
340 disable_count -= 1;
341
342 // If this triggers someone is enabled already enabled interruptsverify( prev != 0u );
343 /* paranoid */ verify( prev != 0u );
344
345 // Check if we need to prempt the thread because an interrupt was missed
346 if( prev == 1 ) {
347 #if GCC_VERSION > 50000
348 static_assert(__atomic_always_lock_free(sizeof(enabled), &enabled), "Must be lock-free");
349 #endif
350
351 // Set enabled flag to true
352 // should be atomic to avoid preemption in the middle of the operation.
353 // use memory order RELAXED since there is no inter-thread on this variable requirements
354 __atomic_store_n(&enabled, true, __ATOMIC_RELAXED);
355
356 // Signal the compiler that a fence is needed but only for signal handlers
357 __atomic_signal_fence(__ATOMIC_RELEASE);
358 if( poll && proc->pending_preemption ) {
359 proc->pending_preemption = false;
360 force_yield( __POLL_PREEMPTION );
361 }
362 }
363 }
364 }
365}
366
367//-----------------------------------------------------------------------------
368// Kernel Signal Debug
369void __cfaabi_check_preemption() {
370 bool ready = __preemption_enabled();
371 if(!ready) { abort("Preemption should be ready"); }
372
373 // __cfaasm_label(debug, before);
374
375 sigset_t oldset;
376 int ret;
377 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
378 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
379
380 ret = sigismember(&oldset, SIGUSR1);
381 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
382 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
383
384 ret = sigismember(&oldset, SIGALRM);
385 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
386 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
387
388 ret = sigismember(&oldset, SIGTERM);
389 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
390 if(ret == 1) { abort("ERROR SIGTERM is disabled"); }
391
392 // __cfaasm_label(debug, after);
393}
394
395#ifdef __CFA_WITH_VERIFY__
396bool __cfaabi_dbg_in_kernel() {
397 return !__preemption_enabled();
398}
399#endif
400
401#undef __cfaasm_label
402
403//-----------------------------------------------------------------------------
404// Signal handling
405
406// sigprocmask wrapper : unblock a single signal
407static inline void signal_unblock( int sig ) {
408 sigset_t mask;
409 sigemptyset( &mask );
410 sigaddset( &mask, sig );
411
412 if ( pthread_sigmask( SIG_UNBLOCK, &mask, 0p ) == -1 ) {
413 abort( "internal error, pthread_sigmask" );
414 }
415}
416
417// sigprocmask wrapper : block a single signal
418static inline void signal_block( int sig ) {
419 sigset_t mask;
420 sigemptyset( &mask );
421 sigaddset( &mask, sig );
422
423 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
424 abort( "internal error, pthread_sigmask" );
425 }
426}
427
428// kill wrapper : signal a processor
429static void preempt( processor * this ) {
430 sigval_t value = { PREEMPT_NORMAL };
431 pthread_sigqueue( this->kernel_thread, SIGUSR1, value );
432}
433
434// reserved for future use
435static void timeout( thread$ * this ) {
436 unpark( this );
437}
438
439void __disable_interrupts_hard() {
440 sigset_t oldset;
441 int ret;
442 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
443 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
444
445 ret = sigismember(&oldset, SIGUSR1);
446 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
447 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
448
449 ret = sigismember(&oldset, SIGALRM);
450 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
451 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
452
453 signal_block( SIGUSR1 );
454}
455
456void __enable_interrupts_hard() {
457 signal_unblock( SIGUSR1 );
458
459 sigset_t oldset;
460 int ret;
461 ret = pthread_sigmask(0, ( const sigset_t * ) 0p, &oldset); // workaround trac#208: cast should be unnecessary
462 if(ret != 0) { abort("ERROR sigprocmask returned %d", ret); }
463
464 ret = sigismember(&oldset, SIGUSR1);
465 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
466 if(ret == 1) { abort("ERROR SIGUSR1 is disabled"); }
467
468 ret = sigismember(&oldset, SIGALRM);
469 if(ret < 0) { abort("ERROR sigismember returned %d", ret); }
470 if(ret == 0) { abort("ERROR SIGALRM is enabled"); }
471}
472
473//-----------------------------------------------------------------------------
474// Some assembly required
475#if defined( __i386 )
476 #ifdef __PIC__
477 #define RELOC_PRELUDE( label ) \
478 "calll .Lcfaasm_prelude_" #label "$pb\n\t" \
479 ".Lcfaasm_prelude_" #label "$pb:\n\t" \
480 "popl %%eax\n\t" \
481 ".Lcfaasm_prelude_" #label "_end:\n\t" \
482 "addl $_GLOBAL_OFFSET_TABLE_+(.Lcfaasm_prelude_" #label "_end-.Lcfaasm_prelude_" #label "$pb), %%eax\n\t"
483 #define RELOC_PREFIX ""
484 #define RELOC_SUFFIX "@GOT(%%eax)"
485 #else
486 #define RELOC_PREFIX "$"
487 #define RELOC_SUFFIX ""
488 #endif
489 #define __cfaasm_label( label ) struct asm_region label = \
490 ({ \
491 struct asm_region region; \
492 asm( \
493 RELOC_PRELUDE( label ) \
494 "movl " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
495 "movl " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
496 : [vb]"=r"(region.before), [va]"=r"(region.after) \
497 ); \
498 region; \
499 });
500#elif defined( __x86_64 )
501 #ifdef __PIC__
502 #define RELOC_PREFIX ""
503 #define RELOC_SUFFIX "@GOTPCREL(%%rip)"
504 #else
505 #define RELOC_PREFIX "$"
506 #define RELOC_SUFFIX ""
507 #endif
508 #define __cfaasm_label( label ) struct asm_region label = \
509 ({ \
510 struct asm_region region; \
511 asm( \
512 "movq " RELOC_PREFIX "__cfaasm_" #label "_before" RELOC_SUFFIX ", %[vb]\n\t" \
513 "movq " RELOC_PREFIX "__cfaasm_" #label "_after" RELOC_SUFFIX ", %[va]\n\t" \
514 : [vb]"=r"(region.before), [va]"=r"(region.after) \
515 ); \
516 region; \
517 });
518#elif defined( __aarch64__ )
519 #ifdef __PIC__
520 // Note that this works only for gcc
521 #define __cfaasm_label( label ) struct asm_region label = \
522 ({ \
523 struct asm_region region; \
524 asm( \
525 "adrp %[vb], _GLOBAL_OFFSET_TABLE_" "\n\t" \
526 "ldr %[vb], [%[vb], #:gotpage_lo15:__cfaasm_" #label "_before]" "\n\t" \
527 "adrp %[va], _GLOBAL_OFFSET_TABLE_" "\n\t" \
528 "ldr %[va], [%[va], #:gotpage_lo15:__cfaasm_" #label "_after]" "\n\t" \
529 : [vb]"=r"(region.before), [va]"=r"(region.after) \
530 ); \
531 region; \
532 });
533 #else
534 #error this is not the right thing to do
535 /*
536 #define __cfaasm_label( label ) struct asm_region label = \
537 ({ \
538 struct asm_region region; \
539 asm( \
540 "adrp %[vb], __cfaasm_" #label "_before" "\n\t" \
541 "add %[vb], %[vb], :lo12:__cfaasm_" #label "_before" "\n\t" \
542 "adrp %[va], :got:__cfaasm_" #label "_after" "\n\t" \
543 "add %[va], %[va], :lo12:__cfaasm_" #label "_after" "\n\t" \
544 : [vb]"=r"(region.before), [va]"=r"(region.after) \
545 ); \
546 region; \
547 });
548 */
549 #endif
550#else
551 #error unknown hardware architecture
552#endif
553
554// KERNEL ONLY
555// Check if a __cfactx_switch signal handler shoud defer
556// If true : preemption is safe
557// If false : preemption is unsafe and marked as pending
558static inline bool preemption_ready( void * ip ) {
559 // Get all the region for which it is not safe to preempt
560 __cfaasm_label( get );
561 __cfaasm_label( check );
562 __cfaasm_label( dsable );
563 // __cfaasm_label( debug );
564
565 // Check if preemption is safe
566 bool ready = true;
567 if( __cfaasm_in( ip, get ) ) { ready = false; goto EXIT; };
568 if( __cfaasm_in( ip, check ) ) { ready = false; goto EXIT; };
569 if( __cfaasm_in( ip, dsable ) ) { ready = false; goto EXIT; };
570 // if( __cfaasm_in( ip, debug ) ) { ready = false; goto EXIT; };
571 if( !__cfaabi_tls.preemption_state.enabled) { ready = false; goto EXIT; };
572 if( __cfaabi_tls.preemption_state.in_progress ) { ready = false; goto EXIT; };
573
574EXIT:
575 // Adjust the pending flag accordingly
576 __cfaabi_tls.this_processor->pending_preemption = !ready;
577 return ready;
578}
579
580//=============================================================================================
581// Kernel Signal Startup/Shutdown logic
582//=============================================================================================
583
584// Startup routine to activate preemption
585// Called from kernel_startup
586void __kernel_alarm_startup() {
587 __cfaabi_dbg_print_safe( "Kernel : Starting preemption\n" );
588
589 // Start with preemption disabled until ready
590 __cfaabi_tls.preemption_state.enabled = false;
591 __cfaabi_tls.preemption_state.disable_count = 1;
592
593 // Initialize the event kernel
594 event_kernel = (event_kernel_t *)&storage_event_kernel;
595 (*event_kernel){};
596
597 // Setup proper signal handlers
598 __cfaabi_sigaction( SIGUSR1, sigHandler_ctxSwitch, SA_SIGINFO ); // __cfactx_switch handler
599 __cfaabi_sigaction( SIGALRM, sigHandler_alarm , SA_SIGINFO ); // debug handler
600
601 signal_block( SIGALRM );
602
603 alarm_stack = __create_pthread( &alarm_thread, alarm_loop, 0p );
604}
605
606// Shutdown routine to deactivate preemption
607// Called from kernel_shutdown
608void __kernel_alarm_shutdown() {
609 __cfaabi_dbg_print_safe( "Kernel : Preemption stopping\n" );
610
611 // Block all signals since we are already shutting down
612 sigset_t mask;
613 sigfillset( &mask );
614 sigprocmask( SIG_BLOCK, &mask, 0p );
615
616 // Notify the alarm thread of the shutdown
617 sigval val;
618 val.sival_int = 0;
619 pthread_sigqueue( alarm_thread, SIGALRM, val );
620
621 // Wait for the preemption thread to finish
622
623 __destroy_pthread( alarm_thread, alarm_stack, 0p );
624
625 // Preemption is now fully stopped
626
627 __cfaabi_dbg_print_safe( "Kernel : Preemption stopped\n" );
628}
629
630// Prevent preemption since we are about to start terminating things
631void __kernel_abort_lock(void) {
632 signal_block( SIGUSR1 );
633}
634
635// Raii ctor/dtor for the preemption_scope
636// Used by thread to control when they want to receive preemption signals
637void ?{}( preemption_scope & this, processor * proc ) {
638 (this.alarm){ proc, 0`s, 0`s };
639 this.proc = proc;
640 this.proc->preemption_alarm = &this.alarm;
641
642 update_preemption( this.proc, this.proc->cltr->preemption_rate );
643}
644
645void ^?{}( preemption_scope & this ) {
646 disable_interrupts();
647
648 update_preemption( this.proc, 0`s );
649}
650
651//=============================================================================================
652// Kernel Signal Handlers
653//=============================================================================================
654__cfaabi_dbg_debug_do( static thread_local void * last_interrupt = 0; )
655
656// Context switch signal handler
657// Receives SIGUSR1 signal and causes the current thread to yield
658static void sigHandler_ctxSwitch( __CFA_SIGPARMS__ ) {
659 void * ip = (void *)(cxt->uc_mcontext.CFA_REG_IP);
660 __cfaabi_dbg_debug_do( last_interrupt = ip; )
661
662 // SKULLDUGGERY: if a thread creates a processor and the immediately deletes it,
663 // the interrupt that is supposed to force the kernel thread to preempt might arrive
664 // before the kernel thread has even started running. When that happens, an interrupt
665 // with a null 'this_processor' will be caught, just ignore it.
666 if(! __cfaabi_tls.this_processor ) return;
667
668 choose(sfp->si_value.sival_int) {
669 case PREEMPT_NORMAL : ;// Normal case, nothing to do here
670 case PREEMPT_TERMINATE: verify( __atomic_load_n( &__cfaabi_tls.this_processor->do_terminate, __ATOMIC_SEQ_CST ) );
671 default:
672 abort( "internal error, signal value is %d", sfp->si_value.sival_int );
673 }
674
675 // Check if it is safe to preempt here
676 if( !preemption_ready( ip ) ) {
677 #if !defined(__CFA_NO_STATISTICS__)
678 __cfaabi_tls.this_stats->ready.threads.preempt.rllfwd++;
679 #endif
680 return;
681 }
682
683 __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) );
684
685 // Sync flag : prevent recursive calls to the signal handler
686 __cfaabi_tls.preemption_state.in_progress = true;
687
688 // Clear sighandler mask before context switching.
689 #if GCC_VERSION > 50000
690 static_assert( sizeof( sigset_t ) == sizeof( cxt->uc_sigmask ), "Expected cxt->uc_sigmask to be of sigset_t" );
691 #endif
692 if ( pthread_sigmask( SIG_SETMASK, (sigset_t *)&(cxt->uc_sigmask), 0p ) == -1 ) {
693 abort( "internal error, sigprocmask" );
694 }
695
696 // Clear the in progress flag
697 __cfaabi_tls.preemption_state.in_progress = false;
698
699 // Preemption can occur here
700
701 #if !defined(__CFA_NO_STATISTICS__)
702 __cfaabi_tls.this_stats->ready.threads.preempt.yield++;
703 #endif
704
705 force_yield( __ALARM_PREEMPTION ); // Do the actual __cfactx_switch
706}
707
708static void sigHandler_alarm( __CFA_SIGPARMS__ ) {
709 abort("SIGALRM should never reach the signal handler");
710}
711
712// Main of the alarm thread
713// Waits on SIGALRM and send SIGUSR1 to whom ever needs it
714static void * alarm_loop( __attribute__((unused)) void * args ) {
715 unsigned id = register_proc_id();
716
717 // Block sigalrms to control when they arrive
718 sigset_t mask;
719 sigfillset(&mask);
720 if ( pthread_sigmask( SIG_BLOCK, &mask, 0p ) == -1 ) {
721 abort( "internal error, pthread_sigmask" );
722 }
723
724 sigemptyset( &mask );
725 sigaddset( &mask, SIGALRM );
726
727 // Main loop
728 while( true ) {
729 // Wait for a sigalrm
730 siginfo_t info;
731 int sig = sigwaitinfo( &mask, &info );
732
733 __cfadbg_print_buffer_decl ( preemption, " KERNEL: sigwaitinfo returned %d, c: %d, v: %d\n", sig, info.si_code, info.si_value.sival_int );
734 __cfadbg_print_buffer_local( preemption, " KERNEL: SI_QUEUE %d, SI_TIMER %d, SI_KERNEL %d\n", SI_QUEUE, SI_TIMER, SI_KERNEL );
735
736 if( sig < 0 ) {
737 //Error!
738 int err = errno;
739 switch( err ) {
740 case EAGAIN :
741 case EINTR :
742 {__cfadbg_print_buffer_local( preemption, " KERNEL: Spurious wakeup %d.\n", err );}
743 continue;
744 case EINVAL :
745 abort( "Timeout was invalid." );
746 default:
747 abort( "Unhandled error %d", err);
748 }
749 }
750
751 // If another signal arrived something went wrong
752 assertf(sig == SIGALRM, "Kernel Internal Error, sigwait: Unexpected signal %d (%d : %d)\n", sig, info.si_code, info.si_value.sival_int);
753
754 // Switch on the code (a.k.a. the sender) to
755 switch( info.si_code )
756 {
757 // Signal was not sent by the kernel but by an other thread
758 case SI_QUEUE:
759 // other threads may signal the alarm thread to shut it down
760 // or to manual cause the preemption tick
761 // use info.si_value and handle the case here
762 switch( info.si_value.sival_int ) {
763 case 0:
764 goto EXIT;
765 default:
766 abort( "SI_QUEUE with val %d", info.si_value.sival_int);
767 }
768 // fallthrough
769 // Timers can apparently be marked as sent for the kernel
770 // In either case, tick preemption
771 case SI_TIMER:
772 case SI_KERNEL:
773 // __cfaabi_dbg_print_safe( "Kernel : Preemption thread tick\n" );
774 lock( event_kernel->lock __cfaabi_dbg_ctx2 );
775 tick_preemption();
776 unlock( event_kernel->lock );
777 break;
778 }
779 }
780
781EXIT:
782 __cfaabi_dbg_print_safe( "Kernel : Preemption thread stopping\n" );
783 unregister_proc_id(id);
784
785 return 0p;
786}
787
788// Local Variables: //
789// mode: c //
790// tab-width: 4 //
791// End: //
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