Date: Sun, 29 Jul 2012 18:04:38 +0000 (UTC) From: Jilles Tjoelker <jilles@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r238888 - head/bin/sh Message-ID: <201207291804.q6TI4cix080438@svn.freebsd.org>
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Author: jilles Date: Sun Jul 29 18:04:38 2012 New Revision: 238888 URL: http://svn.freebsd.org/changeset/base/238888 Log: sh: Fix EINTR race condition in "wait" and "set -T" using sigsuspend(). When waiting for child processes using "wait" or if "set -T" is in effect, a signal interrupts the wait. Make sure there is no window where the signal handler may be invoked (setting a flag) just before going to sleep. There is a similar race condition in the shell language, but scripts can avoid it by exiting from the trap handler or enforcing synchronization using a fifo. If SIGCHLD is not trapped, a signal handler must be installed for it. Only install this handler for the duration of the wait to avoid triggering unexpected [EINTR] errors elsewhere. Note that for some reason only SIGINT and SIGQUIT interrupt a "wait" command. This remains the case. Modified: head/bin/sh/jobs.c head/bin/sh/trap.c head/bin/sh/trap.h Modified: head/bin/sh/jobs.c ============================================================================== --- head/bin/sh/jobs.c Sun Jul 29 14:21:42 2012 (r238887) +++ head/bin/sh/jobs.c Sun Jul 29 18:04:38 2012 (r238888) @@ -87,6 +87,10 @@ int in_waitcmd = 0; /* are we in waitcm 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 */ + #if JOBS static void restartjob(struct job *); #endif @@ -518,7 +522,7 @@ waitcmd(int argc, char **argv) break; } } - } while (dowait(1, (struct job *)NULL) != -1); + } while (dowait(DOWAIT_BLOCK | DOWAIT_SIG, (struct job *)NULL) != -1); in_waitcmd--; return 0; @@ -965,7 +969,7 @@ waitforjob(struct job *jp, int *origstat INTOFF; TRACE(("waitforjob(%%%td) called\n", jp - jobtab + 1)); while (jp->state == 0) - if (dowait(1, jp) == -1) + if (dowait(DOWAIT_BLOCK | (Tflag ? DOWAIT_SIG : 0), jp) == -1) dotrap(); #if JOBS if (jp->jobctl) { @@ -1003,14 +1007,20 @@ waitforjob(struct job *jp, int *origstat } +static void +dummy_handler(int sig) +{ +} /* * Wait for a process to terminate. */ static pid_t -dowait(int block, struct job *job) +dowait(int mode, struct job *job) { + struct sigaction sa, osa; + sigset_t mask, omask; pid_t pid; int status; struct procstat *sp; @@ -1021,8 +1031,22 @@ dowait(int block, struct job *job) int sig; int coredump; int wflags; + int restore_sigchld; TRACE(("dowait(%d) called\n", block)); + restore_sigchld = 0; + if ((mode & DOWAIT_SIG) != 0) { + sigfillset(&mask); + sigprocmask(SIG_BLOCK, &mask, &omask); + INTOFF; + if (!issigchldtrapped()) { + restore_sigchld = 1; + sa.sa_handler = dummy_handler; + sa.sa_flags = 0; + sigemptyset(&sa.sa_mask); + sigaction(SIGCHLD, &sa, &osa); + } + } do { #if JOBS if (iflag) @@ -1030,13 +1054,25 @@ dowait(int block, struct job *job) else #endif wflags = 0; - if (block == 0) + if ((mode & (DOWAIT_BLOCK | DOWAIT_SIG)) != DOWAIT_BLOCK) wflags |= WNOHANG; 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 (int_pending()) + break; + } } while (pid == -1 && errno == EINTR && breakwaitcmd == 0); if (pid == -1 && errno == ECHILD && job != NULL) job->state = JOBDONE; + if ((mode & DOWAIT_SIG) != 0) { + if (restore_sigchld) + sigaction(SIGCHLD, &osa, NULL); + sigprocmask(SIG_SETMASK, &omask, NULL); + INTON; + } if (breakwaitcmd != 0) { breakwaitcmd = 0; if (pid <= 0) Modified: head/bin/sh/trap.c ============================================================================== --- head/bin/sh/trap.c Sun Jul 29 14:21:42 2012 (r238887) +++ head/bin/sh/trap.c Sun Jul 29 18:04:38 2012 (r238888) @@ -368,6 +368,14 @@ ignoresig(int signo) } +int +issigchldtrapped(void) +{ + + return (trap[SIGCHLD] != NULL && *trap[SIGCHLD] != '\0'); +} + + /* * Signal handler. */ Modified: head/bin/sh/trap.h ============================================================================== --- head/bin/sh/trap.h Sun Jul 29 14:21:42 2012 (r238887) +++ head/bin/sh/trap.h Sun Jul 29 18:04:38 2012 (r238888) @@ -41,6 +41,7 @@ void clear_traps(void); int have_traps(void); void setsignal(int); void ignoresig(int); +int issigchldtrapped(void); void onsig(int); void dotrap(void); void setinteractive(int);
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