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Remove async-signal-unsafe code from signal handler #10275

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Remove async-signal-unsafe code from signal handler #10275

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c98f970
remove async-signal-unsafe code from signal handler
TimeToogo Apr 30, 2025
cd29f1b
replace async-signal-unsafe code with safe equivalents
TimeToogo May 9, 2025
2e068d1
store signals in a small ring buffer and process on the main thread
TimeToogo May 10, 2025
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97 changes: 38 additions & 59 deletions src/fluent-bit.c
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@
#include <string.h>
#include <signal.h>
#include <ctype.h>
#include <stdatomic.h>

#include <cfl/cfl.h>
#include <cfl/cfl_array.h>
Expand Down Expand Up @@ -72,6 +73,10 @@ extern void win32_started(void);
flb_ctx_t *ctx;
struct flb_config *config;
volatile sig_atomic_t exit_signal = 0;
#define FLB_MAX_SIGNALS 32
volatile sig_atomic_t caught_signals[FLB_MAX_SIGNALS] = {0};
volatile atomic_uchar caught_signals_write = 0;
volatile atomic_uchar caught_signals_read = 0;
volatile sig_atomic_t flb_bin_restarting = FLB_RELOAD_IDLE;

#ifdef FLB_HAVE_LIBBACKTRACE
Expand Down Expand Up @@ -544,7 +549,7 @@ static void flb_signal_handler_break_loop(int signal)
exit_signal = signal;
}

static void flb_signal_exit(int signal)
static void flb_print_caught_signal(int signal)
{
int len;
char ts[32];
Expand Down Expand Up @@ -577,47 +582,10 @@ static void flb_signal_exit(int signal)
};
}

static void flb_signal_handler_status_line(struct flb_cf *cf_opts)
{
int len;
char ts[32];
char s[] = "[engine] caught signal (";
time_t now;
struct tm *cur;

now = time(NULL);
cur = localtime(&now);
len = snprintf(ts, sizeof(ts) - 1, "[%i/%02i/%02i %02i:%02i:%02i] ",
cur->tm_year + 1900,
cur->tm_mon + 1,
cur->tm_mday,
cur->tm_hour,
cur->tm_min,
cur->tm_sec);

/* write signal number */
write(STDERR_FILENO, ts, len);
write(STDERR_FILENO, s, sizeof(s) - 1);
}

static void flb_signal_handler(int signal)
{
struct flb_cf *cf_opts = flb_cf_context_get();
flb_signal_handler_status_line(cf_opts);

switch (signal) {
flb_print_signal(SIGINT);
#ifndef FLB_SYSTEM_WINDOWS
flb_print_signal(SIGQUIT);
flb_print_signal(SIGHUP);
flb_print_signal(SIGCONT);
#endif
flb_print_signal(SIGTERM);
flb_print_signal(SIGSEGV);
flb_print_signal(SIGFPE);
};

flb_signal_init();
unsigned char cs_write = __atomic_fetch_add(&caught_signals_write, 1, __ATOMIC_SEQ_CST) % FLB_MAX_SIGNALS;
caught_signals[cs_write] = signal;

switch(signal) {
case SIGSEGV:
Expand All @@ -627,21 +595,6 @@ static void flb_signal_handler(int signal)
flb_stacktrace_print(&flb_st);
#endif
abort();
#ifndef FLB_SYSTEM_WINDOWS
case SIGCONT:
flb_dump(ctx->config);
break;
#ifndef FLB_HAVE_STATIC_CONF
case SIGHUP:
if (flb_bin_restarting == FLB_RELOAD_IDLE) {
flb_bin_restarting = FLB_RELOAD_IN_PROGRESS;
}
else {
flb_utils_error(FLB_ERR_RELOADING_IN_PROGRESS);
}
break;
#endif
#endif
}
}

Expand All @@ -664,9 +617,8 @@ static BOOL WINAPI flb_console_handler(DWORD evType)

switch(evType) {
case 0 /* CTRL_C_EVENT_0 */:
cf_opts = flb_cf_context_get();
flb_signal_handler_status_line(cf_opts);
write (STDERR_FILENO, "SIGINT)\n", sizeof("SIGINT)\n")-1);
unsigned char cs_write = __atomic_fetch_add(&caught_signals_write, 1, __ATOMIC_SEQ_CST) % FLB_MAX_SIGNALS;
caught_signals[cs_write] = SIGINT;
/* signal the main loop to execute reload even if CTRL_C event.
* This is necessary because all signal handlers in win32
* are executed on their own thread.
Expand Down Expand Up @@ -1461,10 +1413,37 @@ int flb_main(int argc, char **argv)
sleep(1);
flb_bin_restarting = FLB_RELOAD_IDLE;
}

unsigned char cs_write = __atomic_load_n(&caught_signals_write, __ATOMIC_SEQ_CST);
unsigned char cs_read = __atomic_load_n(&caught_signals_read, __ATOMIC_SEQ_CST);
while (cs_read != cs_write) {
int signal = caught_signals[cs_read % FLB_MAX_SIGNALS];
flb_print_caught_signal(signal);

switch (signal) {
#ifndef FLB_SYSTEM_WINDOWS
case SIGCONT:
flb_dump(ctx->config);
break;
#ifndef FLB_HAVE_STATIC_CONF
case SIGHUP:
if (flb_bin_restarting == FLB_RELOAD_IDLE) {
flb_bin_restarting = FLB_RELOAD_IN_PROGRESS;
}
else {
flb_utils_error(FLB_ERR_RELOADING_IN_PROGRESS);
}
break;
#endif
#endif
}

cs_read = __atomic_fetch_add(&caught_signals_read, 1, __ATOMIC_SEQ_CST) + 1;
}
}

if (exit_signal) {
flb_signal_exit(exit_signal);
flb_print_caught_signal(exit_signal);
}
if (flb_bin_restarting != FLB_RELOAD_ABORTED) {
ret = ctx->config->exit_status_code;
Expand Down