From: Brandon Williams Date: Mon, 10 Apr 2017 23:49:19 GMT Subject: [PATCH 5/5] run-command: add note about forking and threading Message-ID: <20170410234919.34586-6-bmwill@google.com> In-Reply-To: <20170410234919.34586-1-bmwill@google.com> Allocation was pushed before forking in order to avoid potential deadlocking when forking while multiple threads are running. This deadlocking is possible when a thread (other than the one forking) has acquired a lock and didn't get around to releasing it before the fork. This leaves the lock in a locked state in the resulting process with no hope of it ever being released. Signed-off-by: Brandon Williams --- run-command.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/run-command.c b/run-command.c index 84c63b209..2b3249de4 100644 --- a/run-command.c +++ b/run-command.c @@ -458,6 +458,14 @@ int start_command(struct child_process *cmd) argv_array_pushv(&argv, cmd->argv); } + /* + * NOTE: In order to prevent deadlocking when using threads special + * care should be taken with the function calls made in between the + * fork() and exec() calls. No calls should be made to functions which + * require acquiring a lock (e.g. malloc) as the lock could have been + * held by another thread at the time of forking, causing the lock to + * never be released in the child process. + */ cmd->pid = fork(); failed_errno = errno; if (!cmd->pid) { -- 2.12.2.715.g7642488e1d-goog