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sh: Fix race condition with signals and wait or set -T.

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The change in r238888 was incomplete. It was still possible for a trapped
signal to arrive before the shell went to sleep (sigsuspend()) because a
check was missing or because the signal arrived before in_waitcmd was set.

On SMP, this bug sometimes caused the builtins/wait4.0 test to take 1 second
to execute; it then might or might not fail. On UP, the test almost always
failed.
This commit is contained in:
Jilles Tjoelker 2013-09-02 21:57:46 +00:00
parent 42f725eefb
commit b823fb59f1
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=255157
4 changed files with 20 additions and 31 deletions
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32
bin/sh/jobs.c
View File

@ -83,13 +83,12 @@ static struct job *bgjob = NULL; /* last background process */
static struct job *jobmru; /* most recently used job list */
static pid_t initialpgrp; /* pgrp of shell on invocation */
#endif
int in_waitcmd = 0; /* are we in waitcmd()? */
volatile sig_atomic_t breakwaitcmd = 0; /* should wait be terminated? */
static int ttyfd = -1;
/* mode flags for dowait */
#define DOWAIT_BLOCK 0x1 /* wait until a child exits */
#define DOWAIT_SIG 0x2 /* if DOWAIT_BLOCK, abort on signals */
#define DOWAIT_SIG 0x2 /* if DOWAIT_BLOCK, abort on SIGINT/SIGQUIT */
#define DOWAIT_SIG_ANY 0x4 /* if DOWAIT_SIG, abort on any signal */
#if JOBS
static void restartjob(struct job *);
@ -484,7 +483,7 @@ waitcmd(int argc __unused, char **argv __unused)
static int
waitcmdloop(struct job *job)
{
int status, retval;
int status, retval, sig;
struct job *jp;
/*
@ -492,7 +491,6 @@ waitcmdloop(struct job *job)
* received.
*/
in_waitcmd++;
do {
if (job != NULL) {
if (job->state == JOBDONE) {
@ -508,7 +506,6 @@ waitcmdloop(struct job *job)
if (job == bgjob)
bgjob = NULL;
}
in_waitcmd--;
return retval;
}
} else {
@ -524,7 +521,6 @@ waitcmdloop(struct job *job)
}
for (jp = jobtab ; ; jp++) {
if (jp >= jobtab + njobs) { /* no running procs */
in_waitcmd--;
return 0;
}
if (jp->used && jp->state == 0)
@ -532,9 +528,10 @@ waitcmdloop(struct job *job)
}
}
} while (dowait(DOWAIT_BLOCK | DOWAIT_SIG, (struct job *)NULL) != -1);
in_waitcmd--;
return pendingsig + 128;
sig = pendingsig_waitcmd;
pendingsig_waitcmd = 0;
return sig + 128;
}
@ -990,7 +987,8 @@ waitforjob(struct job *jp, int *origstatus)
INTOFF;
TRACE(("waitforjob(%%%td) called\n", jp - jobtab + 1));
while (jp->state == 0)
if (dowait(DOWAIT_BLOCK | (Tflag ? DOWAIT_SIG : 0), jp) == -1)
if (dowait(DOWAIT_BLOCK | (Tflag ? DOWAIT_SIG |
DOWAIT_SIG_ANY : 0), jp) == -1)
dotrap();
#if JOBS
if (jp->jobctl) {
@ -1081,12 +1079,17 @@ dowait(int mode, struct job *job)
pid = wait3(&status, wflags, (struct rusage *)NULL);
TRACE(("wait returns %d, status=%d\n", (int)pid, status));
if (pid == 0 && (mode & DOWAIT_SIG) != 0) {
sigsuspend(&omask);
pid = -1;
if (((mode & DOWAIT_SIG_ANY) != 0 ?
pendingsig : pendingsig_waitcmd) != 0) {
errno = EINTR;
break;
}
sigsuspend(&omask);
if (int_pending())
break;
}
} while (pid == -1 && errno == EINTR && breakwaitcmd == 0);
} while (pid == -1 && errno == EINTR);
if (pid == -1 && errno == ECHILD && job != NULL)
job->state = JOBDONE;
if ((mode & DOWAIT_SIG) != 0) {
@ -1095,11 +1098,6 @@ dowait(int mode, struct job *job)
sigprocmask(SIG_SETMASK, &omask, NULL);
INTON;
}
if (breakwaitcmd != 0) {
breakwaitcmd = 0;
if (pid <= 0)
return -1;
}
if (pid <= 0)
return pid;
INTOFF;

2
bin/sh/jobs.h
View File

@ -83,8 +83,6 @@ enum {
};
extern int job_warning; /* user was warned about stopped jobs */
extern int in_waitcmd; /* are we in waitcmd()? */
extern volatile sig_atomic_t breakwaitcmd; /* break wait to process traps? */
void setjobctl(int);
void showjobs(int, int);

16
bin/sh/trap.c
View File

@ -74,6 +74,7 @@ __FBSDID("$FreeBSD$");
static char sigmode[NSIG]; /* current value of signal */
volatile sig_atomic_t pendingsig; /* indicates some signal received */
volatile sig_atomic_t pendingsig_waitcmd; /* indicates SIGINT/SIGQUIT received */
int in_dotrap; /* do we execute in a trap handler? */
static char *volatile trap[NSIG]; /* trap handler commands */
static volatile sig_atomic_t gotsig[NSIG];
@ -389,23 +390,13 @@ onsig(int signo)
}
/* If we are currently in a wait builtin, prepare to break it */
if ((signo == SIGINT || signo == SIGQUIT) && in_waitcmd != 0) {
breakwaitcmd = 1;
pendingsig = signo;
}
if (signo == SIGINT || signo == SIGQUIT)
pendingsig_waitcmd = signo;
if (trap[signo] != NULL && trap[signo][0] != '\0' &&
(signo != SIGCHLD || !ignore_sigchld)) {
gotsig[signo] = 1;
pendingsig = signo;
/*
* If a trap is set, not ignored and not the null command, we
* need to make sure traps are executed even when a child
* blocks signals.
*/
if (Tflag && !(trap[signo][0] == ':' && trap[signo][1] == '\0'))
breakwaitcmd = 1;
}
#ifndef NO_HISTORY
@ -428,6 +419,7 @@ dotrap(void)
in_dotrap++;
for (;;) {
pendingsig = 0;
pendingsig_waitcmd = 0;
for (i = 1; i < NSIG; i++) {
if (gotsig[i]) {
gotsig[i] = 0;

1
bin/sh/trap.h
View File

@ -34,6 +34,7 @@
*/
extern volatile sig_atomic_t pendingsig;
extern volatile sig_atomic_t pendingsig_waitcmd;
extern int in_dotrap;
extern volatile sig_atomic_t gotwinch;