Subject: + wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process.patch added to -mm tree To: oleg@xxxxxxxxxx,jan.kratochvil@xxxxxxxxxx,lpoetter@xxxxxxxxxx,mschmidt@xxxxxxxxxx,roland@xxxxxxxxxxxxx,tj@xxxxxxxxxx,viro@xxxxxxxxxxxxxxxxxx From: akpm@xxxxxxxxxxxxxxxxxxxx Date: Wed, 26 Feb 2014 15:45:06 -0800 The patch titled Subject: wait: WSTOPPED|WCONTINUED doesn't work if a zombie leader is traced by another process has been added to the -mm tree. Its filename is wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Oleg Nesterov <oleg@xxxxxxxxxx> Subject: wait: WSTOPPED|WCONTINUED doesn't work if a zombie leader is traced by another process Even if the main thread is dead the process still can stop/continue. However, if the leader is ptraced wait_consider_task(ptrace => false) always skips wait_task_stopped/wait_task_continued, so WSTOPPED or WCONTINUED can never work for the natural parent in this case. Move the "A zombie ptracee is only visible to its ptracer" check into the "if (!delay_group_leader(p))" block. ->notask_error is cleared by the "fall through" code below. This depends on the previous change, wait_task_stopped/continued must be avoided if !delay_group_leader() and the tracer is ->real_parent. Otherwise WSTOPPED|WEXITED could wrongly report "stopped" when the child is already dead (single-threaded or not). If it is traced by another task then the "stopped" state is fine until the debugger detaches and reveals a zombie state. Stupid test-case: void *tfunc(void *arg) { sleep(1); // wait for zombie leader raise(SIGSTOP); exit(0x13); return NULL; } int run_child(void) { pthread_t thread; if (!fork()) { int tracee = getppid(); assert(ptrace(PTRACE_ATTACH, tracee, 0,0) == 0); do ptrace(PTRACE_CONT, tracee, 0,0); while (wait(NULL) > 0); return 0; } sleep(1); // wait for PTRACE_ATTACH assert(pthread_create(&thread, NULL, tfunc, NULL) == 0); pthread_exit(NULL); } int main(void) { int child, stat; child = fork(); if (!child) return run_child(); assert(child == waitpid(-1, &stat, WSTOPPED)); assert(stat == 0x137f); kill(child, SIGCONT); assert(child == waitpid(-1, &stat, WCONTINUED)); assert(stat == 0xffff); assert(child == waitpid(-1, &stat, 0)); assert(stat == 0x1300); return 0; } Without this patch it hangs in waitpid(WSTOPPED), wait_task_stopped() is never called. Note: this doesn't fix all problems with a zombie delay_group_leader(), WCONTINUED | WEXITED check is not exactly right. debugger can't assume it will be notified if another thread reaps the whole thread group. Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Jan Kratochvil <jan.kratochvil@xxxxxxxxxx> Cc: Lennart Poettering <lpoetter@xxxxxxxxxx> Cc: Michal Schmidt <mschmidt@xxxxxxxxxx> Cc: Roland McGrath <roland@xxxxxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/exit.c | 22 +++++++++------------- 1 file changed, 9 insertions(+), 13 deletions(-) diff -puN kernel/exit.c~wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process kernel/exit.c --- a/kernel/exit.c~wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process +++ a/kernel/exit.c @@ -1382,20 +1382,16 @@ static int wait_consider_task(struct wai /* slay zombie? */ if (p->exit_state == EXIT_ZOMBIE) { - /* - * A zombie ptracee is only visible to its ptracer. - * Notification and reaping will be cascaded to the real - * parent when the ptracer detaches. - */ - if (likely(!ptrace) && unlikely(p->ptrace)) { - /* it will become visible, clear notask_error */ - wo->notask_error = 0; - return 0; - } - /* we don't reap group leaders with subthreads */ - if (!delay_group_leader(p)) - return wait_task_zombie(wo, p); + if (!delay_group_leader(p)) { + /* + * A zombie ptracee is only visible to its ptracer. + * Notification and reaping will be cascaded to the + * real parent when the ptracer detaches. + */ + if (unlikely(ptrace) || likely(!p->ptrace)) + return wait_task_zombie(wo, p); + } /* * Allow access to stopped/continued state via zombie by _ Patches currently in -mm which might be from oleg@xxxxxxxxxx are kthread-ensure-locality-of-task_struct-allocations.patch mm-revert-thp-make-madv_hugepage-check-for-mm-def_flags.patch mm-thp-add-vm_init_def_mask-and-prctl_thp_disable.patch exec-kill-the-unnecessary-mm-def_flags-setting-in-load_elf_binary.patch exitc-call-proc_exit_connector-after-exit_state-is-set.patch wait-fix-reparent_leader-vs-exit_dead-exit_zombie-race.patch wait-introduce-exit_trace-to-avoid-the-racy-exit_dead-exit_zombie-transition.patch wait-use-exit_trace-only-if-thread_group_leaderzombie.patch wait-completely-ignore-the-exit_dead-tasks.patch wait-swap-exit_zombie-and-exit_dead-to-hide-exit_trace-from-user-space.patch wait-wstoppedwcontinued-hangs-if-a-zombie-child-is-traced-by-real_parent.patch wait-wstoppedwcontinued-doesnt-work-if-a-zombie-leader-is-traced-by-another-process.patch linux-next.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html