8f7b0248a
Denys Vlasenko
2016-10-28
Subject
ash: use pause(), not sigsuspend(), in wait builtin
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shell/ash.c+31 -26
| @@ -296,8 +296,7 @@ struct globals_misc { | |
| volatile int suppress_int; /* counter */ | |
| volatile /*sig_atomic_t*/ smallint pending_int; /* 1 = got SIGINT */ | |
| volatile /*sig_atomic_t*/ smallint got_sigchld; /* 1 = got SIGCHLD */ | |
| - | /* last pending signal */ |
| - | volatile /*sig_atomic_t*/ smallint pending_sig; |
| + | volatile /*sig_atomic_t*/ smallint pending_sig; /* last pending signal */ |
| smallint exception_type; /* kind of exception (0..5) */ | |
| /* exceptions */ | |
| #define EXINT 0 /* SIGINT received */ | |
| @@ -3515,11 +3514,6 @@ setsignal(int signo) | |
| #define CUR_RUNNING 1 | |
| #define CUR_STOPPED 0 | |
| - | /* mode flags for dowait */ |
| - | #define DOWAIT_NONBLOCK 0 |
| - | #define DOWAIT_BLOCK 1 |
| - | #define DOWAIT_BLOCK_OR_SIG 2 |
| - | |
| #if JOBS | |
| /* pgrp of shell on invocation */ | |
| static int initialpgrp; //references:2 | |
| @@ -3940,24 +3934,30 @@ sprint_status48(char *s, int status, int sigonly) | |
| } | |
| static int | |
| - | wait_block_or_sig(int *status, int wait_flags) |
| + | wait_block_or_sig(int *status) |
| { | |
| - | sigset_t mask; |
| int pid; | |
| do { | |
| /* Poll all children for changes in their state */ | |
| got_sigchld = 0; | |
| - | pid = waitpid(-1, status, wait_flags | WNOHANG); |
| + | /* if job control is active, accept stopped processes too */ |
| + | pid = waitpid(-1, status, doing_jobctl ? (WNOHANG|WUNTRACED) : WNOHANG); |
| if (pid != 0) | |
| - | break; /* Error (e.g. EINTR) or pid */ |
| + | break; /* Error (e.g. EINTR, ECHILD) or pid */ |
| - | /* No child is ready. Sleep until interesting signal is received */ |
| + | /* Children exist, but none are ready. Sleep until interesting signal */ |
| + | #if 0 /* dash does this */ |
| + | sigset_t mask; |
| sigfillset(&mask); | |
| sigprocmask(SIG_SETMASK, &mask, &mask); | |
| while (!got_sigchld && !pending_sig) | |
| sigsuspend(&mask); | |
| sigprocmask(SIG_SETMASK, &mask, NULL); | |
| + | #else |
| + | while (!got_sigchld && !pending_sig) |
| + | pause(); |
| + | #endif |
| /* If it was SIGCHLD, poll children again */ | |
| } while (got_sigchld); | |
| @@ -3965,11 +3965,13 @@ wait_block_or_sig(int *status, int wait_flags) | |
| return pid; | |
| } | |
| + | #define DOWAIT_NONBLOCK 0 |
| + | #define DOWAIT_BLOCK 1 |
| + | #define DOWAIT_BLOCK_OR_SIG 2 |
| static int | |
| dowait(int block, struct job *job) | |
| { | |
| - | int wait_flags; |
| int pid; | |
| int status; | |
| struct job *jp; | |
| @@ -3977,13 +3979,6 @@ dowait(int block, struct job *job) | |
| TRACE(("dowait(0x%x) called\n", block)); | |
| - | wait_flags = 0; |
| - | if (block == DOWAIT_NONBLOCK) |
| - | wait_flags = WNOHANG; |
| - | /* If job control is compiled in, we accept stopped processes too. */ |
| - | if (doing_jobctl) |
| - | wait_flags |= WUNTRACED; |
| - | |
| /* It's wrong to call waitpid() outside of INT_OFF region: | |
| * signal can arrive just after syscall return and handler can | |
| * longjmp away, losing stop/exit notification processing. | |
| @@ -3994,17 +3989,27 @@ dowait(int block, struct job *job) | |
| * in INT_OFF region: "wait" needs to wait for any running job | |
| * to change state, but should exit on any trap too. | |
| * In INT_OFF region, a signal just before syscall entry can set | |
| - | * pending_sig valiables, but we can't check them, and we would |
| + | * pending_sig variables, but we can't check them, and we would |
| * either enter a sleeping waitpid() (BUG), or need to busy-loop. | |
| + | * |
| * Because of this, we run inside INT_OFF, but use a special routine | |
| - | * which combines waitpid() and sigsuspend(). |
| + | * which combines waitpid() and pause(). |
| + | * This is the reason why we need to have a handler for SIGCHLD: |
| + | * SIG_DFL handler does not wake pause(). |
| */ | |
| INT_OFF; | |
| - | if (block == DOWAIT_BLOCK_OR_SIG) |
| - | pid = wait_block_or_sig(&status, wait_flags); |
| - | else |
| - | /* NB: _not_ safe_waitpid, we need to detect EINTR. */ |
| + | if (block == DOWAIT_BLOCK_OR_SIG) { |
| + | pid = wait_block_or_sig(&status); |
| + | } else { |
| + | int wait_flags = 0; |
| + | if (block == DOWAIT_NONBLOCK) |
| + | wait_flags = WNOHANG; |
| + | /* if job control is active, accept stopped processes too */ |
| + | if (doing_jobctl) |
| + | wait_flags |= WUNTRACED; |
| + | /* NB: _not_ safe_waitpid, we need to detect EINTR */ |
| pid = waitpid(-1, &status, wait_flags); | |
| + | } |
| TRACE(("wait returns pid=%d, status=0x%x, errno=%d(%s)\n", | |
| pid, status, errno, strerror(errno))); | |
| if (pid <= 0) | |