From 507d7804c0b094889cd20f23ad9a48e2b76791f3 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Fri, 4 Sep 2015 11:35:57 +0200 Subject: pager: don't use unsafe functions in signal handlers Since the commit a3da8821208d (pager: do wait_for_pager on signal death), we call wait_for_pager() in the pager's signal handler. The recent bug report revealed that this causes a deadlock in glibc at aborting "git log" [*1*]. When this happens, git process is left unterminated, and it can't be killed by SIGTERM but only by SIGKILL. The problem is that wait_for_pager() function does more than waiting for pager process's termination, but it does cleanups and printing errors. Unfortunately, the functions that may be used in a signal handler are very limited [*2*]. Particularly, malloc(), free() and the variants can't be used in a signal handler because they take a mutex internally in glibc. This was the cause of the deadlock above. Other than the direct calls of malloc/free, many functions calling malloc/free can't be used. strerror() is such one, either. Also the usage of fflush() and printf() in a signal handler is bad, although it seems working so far. In a safer side, we should avoid them, too. This patch tries to reduce the calls of such functions in signal handlers. wait_for_signal() takes a flag and avoids the unsafe calls. Also, finish_command_in_signal() is introduced for the same reason. There the free() calls are removed, and only waits for the children without whining at errors. [*1*] https://bugzilla.opensuse.org/show_bug.cgi?id=942297 [*2*] http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_04_03 Signed-off-by: Takashi Iwai Reviewed-by: Jeff King Signed-off-by: Junio C Hamano diff --git a/pager.c b/pager.c index 070dc11..0f789c3 100644 --- a/pager.c +++ b/pager.c @@ -14,19 +14,29 @@ static const char *pager_argv[] = { NULL, NULL }; static struct child_process pager_process = CHILD_PROCESS_INIT; -static void wait_for_pager(void) +static void wait_for_pager(int in_signal) { - fflush(stdout); - fflush(stderr); + if (!in_signal) { + fflush(stdout); + fflush(stderr); + } /* signal EOF to pager */ close(1); close(2); - finish_command(&pager_process); + if (in_signal) + finish_command_in_signal(&pager_process); + else + finish_command(&pager_process); +} + +static void wait_for_pager_atexit(void) +{ + wait_for_pager(0); } static void wait_for_pager_signal(int signo) { - wait_for_pager(); + wait_for_pager(1); sigchain_pop(signo); raise(signo); } @@ -90,7 +100,7 @@ void setup_pager(void) /* this makes sure that the parent terminates after the pager */ sigchain_push_common(wait_for_pager_signal); - atexit(wait_for_pager); + atexit(wait_for_pager_atexit); } int pager_in_use(void) diff --git a/run-command.c b/run-command.c index 4d73e90..fe116bc 100644 --- a/run-command.c +++ b/run-command.c @@ -18,26 +18,27 @@ struct child_to_clean { static struct child_to_clean *children_to_clean; static int installed_child_cleanup_handler; -static void cleanup_children(int sig) +static void cleanup_children(int sig, int in_signal) { while (children_to_clean) { struct child_to_clean *p = children_to_clean; children_to_clean = p->next; kill(p->pid, sig); - free(p); + if (!in_signal) + free(p); } } static void cleanup_children_on_signal(int sig) { - cleanup_children(sig); + cleanup_children(sig, 1); sigchain_pop(sig); raise(sig); } static void cleanup_children_on_exit(void) { - cleanup_children(SIGTERM); + cleanup_children(SIGTERM, 0); } static void mark_child_for_cleanup(pid_t pid) @@ -232,7 +233,7 @@ static inline void set_cloexec(int fd) fcntl(fd, F_SETFD, flags | FD_CLOEXEC); } -static int wait_or_whine(pid_t pid, const char *argv0) +static int wait_or_whine(pid_t pid, const char *argv0, int in_signal) { int status, code = -1; pid_t waiting; @@ -240,6 +241,8 @@ static int wait_or_whine(pid_t pid, const char *argv0) while ((waiting = waitpid(pid, &status, 0)) < 0 && errno == EINTR) ; /* nothing */ + if (in_signal) + return 0; if (waiting < 0) { failed_errno = errno; @@ -450,7 +453,7 @@ fail_pipe: * At this point we know that fork() succeeded, but execvp() * failed. Errors have been reported to our stderr. */ - wait_or_whine(cmd->pid, cmd->argv[0]); + wait_or_whine(cmd->pid, cmd->argv[0], 0); failed_errno = errno; cmd->pid = -1; } @@ -549,12 +552,18 @@ fail_pipe: int finish_command(struct child_process *cmd) { - int ret = wait_or_whine(cmd->pid, cmd->argv[0]); + int ret = wait_or_whine(cmd->pid, cmd->argv[0], 0); argv_array_clear(&cmd->args); argv_array_clear(&cmd->env_array); return ret; } +int finish_command_in_signal(struct child_process *cmd) +{ + return wait_or_whine(cmd->pid, cmd->argv[0], 1); +} + + int run_command(struct child_process *cmd) { int code; @@ -785,7 +794,7 @@ error: int finish_async(struct async *async) { #ifdef NO_PTHREADS - return wait_or_whine(async->pid, "child process"); + return wait_or_whine(async->pid, "child process", 0); #else void *ret = (void *)(intptr_t)(-1); diff --git a/run-command.h b/run-command.h index 1103805..518663e 100644 --- a/run-command.h +++ b/run-command.h @@ -50,6 +50,7 @@ void child_process_init(struct child_process *); int start_command(struct child_process *); int finish_command(struct child_process *); +int finish_command_in_signal(struct child_process *); int run_command(struct child_process *); extern const char *find_hook(const char *name); -- cgit v0.10.2-6-g49f6