source: libcfa/src/concurrency/preemption.cfa @ 82a2fed

arm-ehjacob/cs343-translationnew-ast-unique-expr
Last change on this file since 82a2fed was 82a2fed, checked in by Thierry Delisle <tdelisle@…>, 13 months ago

Changed preemption to use code sections rather than atomic access to TLS.

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File size: 25.0 KB
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1//
2// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
3//
4// The contents of this file are covered under the licence agreement in the
5// file "LICENCE" distributed with Cforall.
6//
7// signal.c --
8//
9// Author           : Thierry Delisle
10// Created On       : Mon Jun 5 14:20:42 2017
11// Last Modified By : Peter A. Buhr
12// Last Modified On : 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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