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Re: [PATCH] Fix pldd not to leave process stopped after detaching
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: Andreas Schwab <schwab at suse dot de>, libc-alpha at sourceware dot org
- Date: Mon, 24 Feb 2014 13:49:03 -0500
- Subject: Re: [PATCH] Fix pldd not to leave process stopped after detaching
- Authentication-results: sourceware.org; auth=none
- References: <mvmlhx0bjs1 dot fsf at hawking dot suse dot de>
On 02/24/2014 10:41 AM, Andreas Schwab wrote:
> Wait for the inferior to enter ptrace-stop state before continuing, to
> close a race condition.
>
> Andreas.
>
> [BZ #15804]
> * elf/pldd.c (wait_for_ptrace_stop): New function.
> (main): Call it after attaching.
Looks good to me, and better than what we had before.
Note:
At some point we should reimplement this as PTRACE_SEIZE
and PTRACE_INTERRUPT if the minimum kernel is 3.4 or newer
which solves the still existing race conditions where
SIG_STOP could be lost and we can ignore the need to reinject
signals and check for errors.
> ---
> elf/pldd.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/elf/pldd.c b/elf/pldd.c
> index 684aff4..75f7812 100644
> --- a/elf/pldd.c
> +++ b/elf/pldd.c
> @@ -34,6 +34,7 @@
> #include <unistd.h>
> #include <sys/ptrace.h>
> #include <sys/stat.h>
> +#include <sys/wait.h>
>
> #include <ldsodefs.h>
> #include <version.h>
> @@ -82,6 +83,7 @@ static char *exe;
>
> /* Local functions. */
> static int get_process_info (int dfd, long int pid);
> +static void wait_for_ptrace_stop (long int pid);
>
>
> int
> @@ -170,6 +172,8 @@ main (int argc, char *argv[])
> tid);
> }
>
> + wait_for_ptrace_stop (tid);
> +
> struct thread_list *newp = alloca (sizeof (*newp));
> newp->tid = tid;
> newp->next = thread_list;
> @@ -194,6 +198,27 @@ main (int argc, char *argv[])
> }
>
>
> +/* Wait for PID to enter ptrace-stop state after being attached. */
> +static void
> +wait_for_ptrace_stop (long int pid)
> +{
> + int status;
> +
> + /* While waiting for SIGSTOP being delivered to the tracee we have to
> + reinject any other pending signal. Ignore all other errors. */
> + while (waitpid (pid, &status, __WALL) == pid && WIFSTOPPED (status))
> + {
> + /* The STOP signal should not be delivered to the tracee. */
> + if (WSTOPSIG (status) == SIGSTOP)
> + return;
> + if (ptrace (PTRACE_CONT, pid, NULL,
> + (void *) (uintptr_t) WSTOPSIG (status)))
> + /* The only possible error is that the process died. */
> + return;
> + }
> +}
> +
> +
> /* Handle program arguments. */
> static error_t
> parse_opt (int key, char *arg, struct argp_state *state)
>