From 13c4d8aba5eca5f0d70a42661731d2de6bdc02a4 Mon Sep 17 00:00:00 2001 From: =?utf8?q?J=C3=A9r=C3=A9mie=20Galarneau?= Date: Fri, 16 Oct 2020 14:43:39 -0400 Subject: [PATCH] Fix: common: poll: compat_poll_wait never finishes MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit compat_poll_wait hangs when poll returns an array of file descriptors of the form: [ Inactive Active ] The logic to find the first idle pollfd entry is bogus and actually skips the first idle entry. This causes the follow-up loop to never conclude. The pollfd array defragmentation logic is re-written in a simpler style to handle those cases appropriately. Signed-off-by: Jérémie Galarneau Change-Id: I8669a870df1ec1160f05e35e83671917bb80d6f9 --- src/common/compat/compat-poll.c | 47 +++++++++++++++++---------------- 1 file changed, 24 insertions(+), 23 deletions(-) diff --git a/src/common/compat/compat-poll.c b/src/common/compat/compat-poll.c index 79756f573..499a27623 100644 --- a/src/common/compat/compat-poll.c +++ b/src/common/compat/compat-poll.c @@ -307,8 +307,7 @@ int compat_poll_wait(struct lttng_poll_event *events, int timeout, bool interruptible) { int ret, active_fd_count; - int idle_pfd_index = 0; - size_t i; + size_t pos = 0, consecutive_entries = 0, non_idle_pos; if (events == NULL || events->current.events == NULL) { ERR("poll wait arguments error"); @@ -344,34 +343,36 @@ int compat_poll_wait(struct lttng_poll_event *events, int timeout, active_fd_count = ret; /* - * Swap all active pollfd structs to the beginning of the - * array to emulate compat-epoll behaviour. This algorithm takes - * advantage of poll's returned value and the burst nature of active - * events on the file descriptors. The while loop guarantees that - * idle_pfd will always point to an idle fd. + * Move all active pollfd structs to the beginning of the + * array to emulate compat-epoll behaviour. */ if (active_fd_count == events->wait.nb_fd) { goto end; } - while (idle_pfd_index < active_fd_count && - events->wait.events[idle_pfd_index].revents != 0) { - idle_pfd_index++; - } - for (i = idle_pfd_index + 1; idle_pfd_index < active_fd_count; - i++) { - struct pollfd swap_pfd; - struct pollfd *idle_pfd = &events->wait.events[idle_pfd_index]; - struct pollfd *current_pfd = &events->wait.events[i]; - - if (idle_pfd->revents != 0) { - swap_pfd = *current_pfd; - *current_pfd = *idle_pfd; - *idle_pfd = swap_pfd; - idle_pfd_index++; + while (consecutive_entries != active_fd_count) { + struct pollfd *current = &events->wait.events[pos]; + struct pollfd idle_entry; + + if (current->revents != 0) { + consecutive_entries++; + pos++; + continue; } - } + non_idle_pos = pos; + + /* Look for next non-idle entry. */ + while (events->wait.events[++non_idle_pos].revents == 0); + + /* Swap idle and non-idle entries. */ + idle_entry = *current; + *current = events->wait.events[non_idle_pos]; + events->wait.events[non_idle_pos] = idle_entry; + + consecutive_entries++; + pos++; + } end: return ret; -- 2.34.1