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9868c2081d
Changing os_idle_sleep() to use pause() (I accidentally described
it as an empty select() in the commit log because I had changed it
from that to pause() in a later revision) exposed a race condition
in the idle code. The following can happen:
timer_settime(0, 0, {it_interval={tv_sec=0, tv_nsec=0}, it_value={tv_sec=0, tv_nsec=624017}}, NULL) = 0
...
<SIGALRM is delivered but we're already on the way to idle>
pause()
and we now hang forever. This was previously possible as well, but
it could never cause UML to hang for more than a second since we
could only sleep for that much, so at most you'd notice a "hiccup"
in the UML. Obviously, any sort of external interrupt also "saves"
it and interrupts pause().
Fix this by properly handling the race, rather than papering over
it again:
- first, block SIGALRM, and obtain the old signal set
- check the timer
- suspend, waiting for any signal out of the old set, if, and only
if, the timer will fire in the future
- restore the old signal mask
This ensures race-free operation: as it's blocked, the signal won't
be delivered while we're looking at the timer even if it were to be
triggered right _after_ we've returned from timer_gettime() with a
non-zero value (telling us the timer will trigger). Thus, despite
getting to sigsuspend() because timer_gettime() told us we're still
waiting, we'll not hang because sigsuspend() will return immediately
due to the pending signal.
Fixes: 49da38a3ef ("um: Simplify os_idle_sleep() and sleep longer")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
122 lines
2.7 KiB
C
122 lines
2.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
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* Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
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* Copyright (C) 2012-2014 Cisco Systems
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* Copyright (C) 2000 - 2007 Jeff Dike (jdike{addtoit,linux.intel}.com)
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*/
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#include <stddef.h>
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#include <unistd.h>
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#include <errno.h>
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#include <signal.h>
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#include <time.h>
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#include <sys/time.h>
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#include <kern_util.h>
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#include <os.h>
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#include <string.h>
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static timer_t event_high_res_timer = 0;
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static inline long long timeval_to_ns(const struct timeval *tv)
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{
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return ((long long) tv->tv_sec * UM_NSEC_PER_SEC) +
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tv->tv_usec * UM_NSEC_PER_USEC;
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}
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static inline long long timespec_to_ns(const struct timespec *ts)
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{
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return ((long long) ts->tv_sec * UM_NSEC_PER_SEC) + ts->tv_nsec;
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}
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long long os_persistent_clock_emulation(void)
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{
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struct timespec realtime_tp;
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clock_gettime(CLOCK_REALTIME, &realtime_tp);
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return timespec_to_ns(&realtime_tp);
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}
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/**
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* os_timer_create() - create an new posix (interval) timer
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*/
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int os_timer_create(void)
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{
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timer_t *t = &event_high_res_timer;
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if (timer_create(CLOCK_MONOTONIC, NULL, t) == -1)
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return -1;
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return 0;
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}
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int os_timer_set_interval(unsigned long long nsecs)
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{
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struct itimerspec its;
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its.it_value.tv_sec = nsecs / UM_NSEC_PER_SEC;
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its.it_value.tv_nsec = nsecs % UM_NSEC_PER_SEC;
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its.it_interval.tv_sec = nsecs / UM_NSEC_PER_SEC;
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its.it_interval.tv_nsec = nsecs % UM_NSEC_PER_SEC;
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if (timer_settime(event_high_res_timer, 0, &its, NULL) == -1)
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return -errno;
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return 0;
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}
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int os_timer_one_shot(unsigned long long nsecs)
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{
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struct itimerspec its = {
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.it_value.tv_sec = nsecs / UM_NSEC_PER_SEC,
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.it_value.tv_nsec = nsecs % UM_NSEC_PER_SEC,
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.it_interval.tv_sec = 0,
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.it_interval.tv_nsec = 0, // we cheat here
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};
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timer_settime(event_high_res_timer, 0, &its, NULL);
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return 0;
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}
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/**
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* os_timer_disable() - disable the posix (interval) timer
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*/
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void os_timer_disable(void)
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{
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struct itimerspec its;
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memset(&its, 0, sizeof(struct itimerspec));
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timer_settime(event_high_res_timer, 0, &its, NULL);
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}
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long long os_nsecs(void)
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{
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struct timespec ts;
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clock_gettime(CLOCK_MONOTONIC,&ts);
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return timespec_to_ns(&ts);
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}
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/**
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* os_idle_sleep() - sleep until interrupted
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*/
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void os_idle_sleep(void)
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{
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struct itimerspec its;
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sigset_t set, old;
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/* block SIGALRM while we analyze the timer state */
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sigemptyset(&set);
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sigaddset(&set, SIGALRM);
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sigprocmask(SIG_BLOCK, &set, &old);
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/* check the timer, and if it'll fire then wait for it */
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timer_gettime(event_high_res_timer, &its);
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if (its.it_value.tv_sec || its.it_value.tv_nsec)
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sigsuspend(&old);
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/* either way, restore the signal mask */
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sigprocmask(SIG_UNBLOCK, &set, NULL);
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}
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