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 --- pager.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) (limited to 'pager.c') diff --git a/pager.c b/pager.c index 070dc11cb0..0f789c3ed4 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) -- cgit v1.2.3