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Disable automatic suspend when MCE process exits
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We must not leave the device in early suspend mode when the
MCE process exits.

Added an atexit handler for blocking suspend on normal exits.

Added SIGSEGV etc handlers that attempt to block suspend if
mce happens to crash.

Refactored signal handling to pass signals via pipe to be
processed outside the async signal handler context.

Added mce_abort() function that should be used instead of
_exit() and abort() in mce code.
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@spiiroin
spiiroin committed Dec 11, 2012
1 parent 56ef4e5 commit 8d01830
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Showing 3 changed files with 257 additions and 10 deletions.
2 changes: 2 additions & 0 deletions .depend
View file
Expand Up @@ -195,6 +195,7 @@ mce.o:\
datapipe.h\
event-input.h\
event-switches.h\
libwakelock.h\
mce-conf.h\
mce-dbus.h\
mce-dsme.h\
Expand All @@ -211,6 +212,7 @@ mce.pic.o:\
datapipe.h\
event-input.h\
event-switches.h\
libwakelock.h\
mce-conf.h\
mce-dbus.h\
mce-dsme.h\
Expand Down
263 changes: 253 additions & 10 deletions mce.c
View file
Expand Up @@ -130,6 +130,9 @@
#include "powerkey.h" /* mce_powerkey_init(),
* mce_powerkey_exit()
*/
#ifdef ENABLE_WAKELOCKS
# include "libwakelock.h"
#endif

/** Path to the lockfile */
#define MCE_LOCKFILE "/var/run/mce.pid"
Expand All @@ -141,6 +144,24 @@ extern char *optarg; /**< Used by getopt */

static const gchar *progname; /**< Used to store the name of the program */

/** Wrapper for write() for use when we do not care if it works or not
*
* Main purpose is to stop static analyzers from nagging us when
* we really do not care whether the data gets written or not
*
* @param fd file descriptor to write to
* @param data data to write
* @param size amount of data to write
*/
static void no_error_check_write(int fd, const void *data, size_t size)
{
// do the write, then ...
ssize_t rc = TEMP_FAILURE_RETRY(write(fd, data, size));
// try to silence static analyzers by doing /something/ with rc
if( rc == -1 )
rc = rc;
}

/**
* Display usage information
*/
Expand Down Expand Up @@ -229,6 +250,61 @@ static gint init_locales(const gchar *const name)
return status;
}

#ifdef ENABLE_WAKELOCKS
/** Disable automatic suspend and remove wakelocks mce might hold
*
* This function should be called just before mce process terminates
* so that we do not leave the system in a non-functioning state
*/
static void mce_cleanup_wakelocks(void)
{
/* FIXME: since this gets called from signal handler too,
* all wakelock functions should be made async-signal-safe.
* At the moment they use at least fprintf() and snprintf()
* that are not safe.
*/

wakelock_block_suspend();
wakelock_unlock("mce_display_on");
wakelock_unlock("mce_input_handler");
}
#endif // ENABLE_WAKELOCKS

/** Disable autosuspend then exit via default signal handler
*
* @param signr the signal to exit through
*/
static void mce_exit_via_signal(int signr) __attribute__((noreturn));
static void mce_exit_via_signal(int signr)
{
/* Give us N seconds to exit */
signal(SIGALRM, SIG_DFL);
alarm(3);

/* Restore default behavior */
signal(signr, SIG_DFL);

#ifdef ENABLE_WAKELOCKS
/* Cancel auto suspend */
mce_cleanup_wakelocks();
#endif

/* Exit via default handler or abort() */
raise(signr);
abort();
}

/** Suspend safe replacement for _exit(1), abort() etc
*/
void mce_abort(void)
{
#ifdef ENABLE_WAKELOCKS
mce_exit_via_signal(SIGABRT);
#else
abort();
#endif
}

/**
* Signal handler
*
Expand All @@ -245,8 +321,32 @@ static void signal_handler(const gint signr)
/* Possibly for re-reading configuration? */
break;

#ifdef ENABLE_WAKELOCKS
case SIGABRT:
case SIGILL:
case SIGFPE:
case SIGSEGV:
case SIGPIPE:
case SIGALRM:
case SIGBUS:
/* Terminating, but disable suspend first */
mce_exit_via_signal(signr);
break;

case SIGTSTP:
/* Stopping mce could also lead to unrecoverable suspend */
break;
#endif

case SIGINT:
case SIGQUIT:
case SIGTERM:
/* This should be done through a pipe or signalfd instead */
/* Just die if we somehow get here without having a mainloop */
if( !mainloop ) {
mce_exit_via_signal(signr);
}

/* Terminate mainloop */
g_main_loop_quit(mainloop);
break;

Expand All @@ -256,6 +356,134 @@ static void signal_handler(const gint signr)
}
}

/** Install handlers for signals we need to trap
*/
static void install_signal_handlers(void)
{
static const int sig[] = {
SIGUSR1,
SIGHUP,

SIGINT,
SIGQUIT,
SIGTERM,

#ifdef ENABLE_WAKELOCKS
SIGABRT,
SIGILL,
SIGFPE,
SIGSEGV,
SIGPIPE,
SIGALRM,
SIGBUS,
SIGTSTP,
#endif

-1
};

for( size_t i = 0; sig[i] != -1; ++i ) {
signal(sig[i], mce_tx_signal_cb);
}
}

/** Pipe used for transferring signals out of signal handler context */
static int signal_pipe[2] = {-1, -1};

/** GIO callback for reading signals from pipe
*
* @param channel io channel for signal pipe
* @param condition call reason
* @param data user data
*
* @return TRUE (or aborts on error)
*/
static gboolean mce_rx_signal_cb(GIOChannel *channel,
GIOCondition condition, gpointer data)
{
// we just want the cb ...
(void)channel; (void)condition; (void)data;

int sig = 0;
int got = TEMP_FAILURE_RETRY(read(signal_pipe[0], &sig, sizeof sig));

if( got != sizeof sig ) {
mce_abort();
}

/* handle the signal */
signal_handler(sig);

/* keep the io watch */
return TRUE;
}

/** Signal handler callback for writing signals to pipe
*
* @param sig the signal number to pass to mainloop via pipe
*/
static void mce_tx_signal_cb(int sig)
{
/* NOTE: this function must be kept async-signal-safe! */

static volatile int exit_tries = 0;

static const char msg[] = "\n*** BREAK ***\n";

/* FIXME: Should really use sigaction() to avoid having
* the default handler active until we manage to restore
* our handler here ... */
signal(sig, mce_tx_signal_cb);

/* Make sure that a stuck or non-existing mainloop does not stop
* us from handling at least repeated terminating signals */
switch( sig )
{
case SIGINT:
case SIGQUIT:
case SIGTERM:
no_error_check_write(STDERR_FILENO, msg, sizeof msg - 1);

if( !mainloop || ++exit_tries >= 2 ) {
mce_abort();
}
break;
default:
break;
}

/* transfer the signal to mainloop via pipe */
int did = TEMP_FAILURE_RETRY(write(signal_pipe[1], &sig, sizeof sig));

if( did != (int)sizeof sig ) {
mce_abort();
}
}

/** Create a pipe and io watch for handling signal from glib mainloop
*/
static gboolean mce_init_signal_pipe(void)
{
int result = FALSE;
GIOChannel *channel = 0;

if( pipe(signal_pipe) == -1 )
goto EXIT;

if( (channel = g_io_channel_unix_new(signal_pipe[0])) == 0 )
goto EXIT;

if( !g_io_add_watch(channel, G_IO_IN, mce_rx_signal_cb, 0) )
goto EXIT;

result = TRUE;

EXIT:
if( channel != 0 ) g_io_channel_unref(channel);

return result;
}

/**
* Daemonize the program
*
Expand All @@ -273,7 +501,7 @@ static gboolean daemonize(void)
/* Detach from process group */
switch (fork()) {
case -1:
/* Failure */
/* Parent - Failure */
mce_log(LL_CRIT, "daemonize: fork failed: %s",
g_strerror(errno));
mce_log_close();
Expand All @@ -284,8 +512,11 @@ static gboolean daemonize(void)
break;

default:
/* Parent -- exit */
exit(EXIT_SUCCESS);
/* Parent -- Success */

/* One main() one exit() - in this case the parent
* must not call atexit handlers etc */
_exit(EXIT_SUCCESS);
}

/* Detach TTY */
Expand Down Expand Up @@ -379,7 +610,7 @@ static gboolean daemonize(void)
}

sprintf(str, "%d\n", getpid());
write(i, str, strlen(str));
no_error_check_write(i, str, strlen(str));
close(i);

/* Ignore TTY signals */
Expand Down Expand Up @@ -520,20 +751,29 @@ int main(int argc, char **argv)
mce_log_open(PRG_NAME, LOG_DAEMON, logtype);
mce_log_set_verbosity(verbosity);

#ifdef ENABLE_WAKELOCKS
/* Since mce enables automatic suspend, we must try to
* disable it when mce process exits */
atexit(mce_cleanup_wakelocks);
#endif

/* Daemonize if requested */
if (daemonflag == TRUE)
daemonize();

signal(SIGUSR1, signal_handler);
signal(SIGHUP, signal_handler);
signal(SIGTERM, signal_handler);

/* Initialise GType system */
g_type_init();

/* Register a mainloop */
mainloop = g_main_loop_new(NULL, FALSE);

/* Signal handlers can be installed once we have a mainloop */
if( !mce_init_signal_pipe() ) {
mce_log(LL_CRIT, "Failed to initialise signal pipe");
exit(EXIT_FAILURE);
}
install_signal_handlers();

/* Initialise subsystems */

/* Get configuration options */
Expand Down Expand Up @@ -747,7 +987,10 @@ int main(int argc, char **argv)

/* Log a farewell message and close the log */
mce_log(LL_INFO, "Exiting...");
mce_log_close();

/* We do not need to explicitly close the log and doing so
* would not allow logging from atexit handlers */
//mce_log_close();

return status;
}
2 changes: 2 additions & 0 deletions mce.h
View file
Expand Up @@ -349,4 +349,6 @@ submode_t mce_get_submode_int32(void);
gboolean mce_add_submode_int32(const submode_t submode);
gboolean mce_rem_submode_int32(const submode_t submode);

void mce_abort(void) __attribute__((noreturn));

#endif /* _MCE_H_ */

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