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pager: don't use unsafe functions in signal handlers

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Since the commit a3da882120 (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 <tiwai@suse.de>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Takashi Iwai
2015-09-04 11:35:57 +02:00
committed by Junio C Hamano
parent a17c56c056
commit 507d7804c0
3 changed files with 34 additions and 14 deletions
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22
pager.c
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@ -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)