shell: fix race between signal handlers setting bb_got_signal and poll()

function                                             old     new   delta
__ppoll_time64                                         -     211    +211
check_got_signal_and_poll                              -     164    +164
read_key                                             607     601      -6
shell_builtin_read                                  1328    1318     -10
------------------------------------------------------------------------------
(add/remove: 4/0 grow/shrink: 0/2 up/down: 375/-16)           Total: 359 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/shell/shell_common.c b/shell/shell_common.c
index 2baa9d3a8..754fef34b 100644
--- a/shell/shell_common.c
+++ b/shell/shell_common.c
@@ -214,12 +214,13 @@ shell_builtin_read(struct builtin_read_params *params)
                  * regardless of SA_RESTART-ness of that signal!
                  */
                 errno = 0;
-                pfd[0].events = POLLIN;
-//TODO race with a signal arriving just before the poll!
-                if (poll(pfd, 1, timeout) <= 0) {
+                pfd->events = POLLIN;
+
+                /* test bb_got_signal, then poll(), atomically wrt signals */
+                if (check_got_signal_and_poll(pfd, timeout) <= 0) {
                         /* timed out, or some error */
                         err = errno;
-                        if (!err) {
+                        if (!err) { /* timed out */
                                 retval = (const char *)(uintptr_t)2;
                                 break;
                         }