From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756139Ab1E2XNb (ORCPT ); Sun, 29 May 2011 19:13:31 -0400 Received: from mail-bw0-f46.google.com ([209.85.214.46]:56170 "EHLO mail-bw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755849Ab1E2XNN (ORCPT ); Sun, 29 May 2011 19:13:13 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:from:to:cc:subject:date:message-id:x-mailer:in-reply-to :references; b=R1HkHtQ1mCeTUJTtm5hZIsagMncdzY7l5hvZSJ7kBJRgGpu70zgsfrU8WSFWhIRMYG KkYnbh5sgIpJVFQMYfim/Lc0f0JwlI+jTqcDYBz//xdtFtqZGCB2nVR89JcafKYtW0vN z1LHHgmk45QuAGBq9pvXkOx7vWizpEgg4wMgM= From: Tejun Heo To: oleg@redhat.com Cc: vda.linux@googlemail.com, jan.kratochvil@redhat.com, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, indan@nul.nu, bdonlan@gmail.com, pedro@codesourcery.com, Tejun Heo Subject: [PATCH 16/17] ptrace: implement TRAP_NOTIFY and use it for group stop events Date: Mon, 30 May 2011 01:12:39 +0200 Message-Id: <1306710760-16440-17-git-send-email-tj@kernel.org> X-Mailer: git-send-email 1.7.5.2 In-Reply-To: <1306710760-16440-1-git-send-email-tj@kernel.org> References: <1306710760-16440-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently there's no way for ptracer to find out whether group stop finished other than polling with INTERRUPT - GETSIGINFO - CONT sequence This patch implements group stop notification for ptracer using STOP traps. When group stop state of a seized tracee changes, JOBCTL_TRAP_NOTIFY is set, which schedules a STOP trap which is sticky - it isn't cleared by other traps and at least one STOP trap will happen eventually. STOP trap is synchronization point for event notification and ptracer is required to fetch group stop information with PTRACE_GETSIGINFO on each STOP trap if it intends to keep track of group stop changes. Notifications are generated both on start and end of group stops but, because group stop participation always happens before STOP trap, this doesn't cause an extra trap while tracee is participating in group stop. The symmetry will be useful later. Note that this notification works iff tracee is not trapped. Currently there is no way to be notified of group stop state changes while tracee is trapped. This will be addressed by a later patch. An example program follows. #define PTRACE_SEIZE 0x4206 #define PTRACE_INTERRUPT 0x4207 #define PTRACE_SEIZE_DEVEL 0x80000000 static const struct timespec ts1s = { .tv_sec = 1 }; int main(int argc, char **argv) { pid_t tracee, tracer; int i; tracee = fork(); if (!tracee) while (1) pause(); tracer = fork(); if (!tracer) { int stopped; siginfo_t si; ptrace(PTRACE_SEIZE, tracee, NULL, (void *)(unsigned long)PTRACE_SEIZE_DEVEL); ptrace(PTRACE_INTERRUPT, tracee, NULL, NULL); repeat: waitid(P_PID, tracee, NULL, WSTOPPED); ptrace(PTRACE_GETSIGINFO, tracee, NULL, &si); if (!si.si_code) { printf("tracer: SIG %d\n", si.si_signo); ptrace(PTRACE_CONT, tracee, NULL, (void *)(unsigned long)si.si_signo); goto repeat; } stopped = !!si.si_status; printf("tracer: stopped=%d signo=%d\n", stopped, si.si_signo); ptrace(PTRACE_CONT, tracee, NULL, NULL); goto repeat; } for (i = 0; i < 3; i++) { nanosleep(&ts1s, NULL); printf("mother: SIGSTOP\n"); kill(tracee, SIGSTOP); nanosleep(&ts1s, NULL); printf("mother: SIGCONT\n"); kill(tracee, SIGCONT); } nanosleep(&ts1s, NULL); kill(tracer, SIGKILL); kill(tracee, SIGKILL); return 0; } In the above program, tracer keeps tracee running and gets notification of each group stop state changes. # ./test-notify tracer: stopped=0 signo=5 mother: SIGSTOP tracer: SIG 19 tracer: stopped=1 signo=19 mother: SIGCONT tracer: stopped=0 signo=5 tracer: SIG 18 mother: SIGSTOP tracer: SIG 19 tracer: stopped=1 signo=19 mother: SIGCONT tracer: stopped=0 signo=5 tracer: SIG 18 mother: SIGSTOP tracer: SIG 19 tracer: stopped=1 signo=19 mother: SIGCONT tracer: stopped=0 signo=5 tracer: SIG 18 Signed-off-by: Tejun Heo Cc: Oleg Nesterov --- include/linux/ptrace.h | 2 ++ include/linux/sched.h | 4 +++- kernel/signal.c | 38 +++++++++++++++++++++++++++++++++++--- 3 files changed, 40 insertions(+), 4 deletions(-) diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h index f16a63f..43f762d 100644 --- a/include/linux/ptrace.h +++ b/include/linux/ptrace.h @@ -73,6 +73,8 @@ #define PTRACE_EVENT_EXIT 6 #define PTRACE_EVENT_STOP 7 +#define PTRACE_STOP_SI_CODE (__SI_TRAP | SIGTRAP | PTRACE_EVENT_STOP << 8) + /* flags in siginfo.si_pt_flags from PTRACE_GETSIGINFO */ #define PTRACE_SI_STOPPED 0x00000001 /* tracee is job control stopped */ diff --git a/include/linux/sched.h b/include/linux/sched.h index 20f392b..161658f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1811,15 +1811,17 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t * #define JOBCTL_STOP_PENDING_BIT 17 /* task should stop for group stop */ #define JOBCTL_STOP_CONSUME_BIT 18 /* consume group stop count */ #define JOBCTL_TRAP_STOP_BIT 19 /* trap for STOP */ +#define JOBCTL_TRAP_NOTIFY_BIT 20 /* trap for NOTIFY */ #define JOBCTL_TRAPPING_BIT 21 /* switching to TRACED */ #define JOBCTL_STOP_DEQUEUED (1 << JOBCTL_STOP_DEQUEUED_BIT) #define JOBCTL_STOP_PENDING (1 << JOBCTL_STOP_PENDING_BIT) #define JOBCTL_STOP_CONSUME (1 << JOBCTL_STOP_CONSUME_BIT) #define JOBCTL_TRAP_STOP (1 << JOBCTL_TRAP_STOP_BIT) +#define JOBCTL_TRAP_NOTIFY (1 << JOBCTL_TRAP_NOTIFY_BIT) #define JOBCTL_TRAPPING (1 << JOBCTL_TRAPPING_BIT) -#define JOBCTL_TRAP_MASK JOBCTL_TRAP_STOP +#define JOBCTL_TRAP_MASK (JOBCTL_TRAP_STOP | JOBCTL_TRAP_NOTIFY) #define JOBCTL_PENDING_MASK (JOBCTL_STOP_PENDING | JOBCTL_TRAP_MASK) extern bool task_set_jobctl_pending(struct task_struct *task, diff --git a/kernel/signal.c b/kernel/signal.c index c6ebdfe..5a72324 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -817,6 +817,30 @@ static int check_kill_permission(int sig, struct siginfo *info, return security_task_kill(t, info, sig, 0); } +/** + * ptrace_trap_notify - schedule trap to notify ptracer + * @t: tracee wanting to notify tracer + * + * This function schedules sticky ptrace trap which is cleared on the next + * TRAP_STOP to notify ptracer of an event. @t must have been seized by + * ptracer. + * + * If @t is running, STOP trap will be taken. If already trapped, STOP + * trap will be eventually taken without returning to userland after the + * existing traps are finished by PTRACE_CONT. + * + * CONTEXT: + * Must be called with @task->sighand->siglock held. + */ +static void ptrace_trap_notify(struct task_struct *t) +{ + WARN_ON_ONCE(!(t->ptrace & PT_SEIZED)); + assert_spin_locked(&t->sighand->siglock); + + task_set_jobctl_pending(t, JOBCTL_TRAP_NOTIFY); + signal_wake_up(t, 0); +} + /* * Handle magic process-wide effects of stop/continue signals. Unlike * the signal actions, these happen immediately at signal-generation @@ -855,7 +879,10 @@ static int prepare_signal(int sig, struct task_struct *p, int from_ancestor_ns) do { task_clear_jobctl_pending(t, JOBCTL_STOP_PENDING); rm_from_queue(SIG_KERNEL_STOP_MASK, &t->pending); - wake_up_state(t, __TASK_STOPPED); + if (likely(!(t->ptrace & PT_SEIZED))) + wake_up_state(t, __TASK_STOPPED); + else + ptrace_trap_notify(t); } while_each_thread(p, t); /* @@ -1797,8 +1824,10 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info) if (why == CLD_STOPPED && (current->jobctl & JOBCTL_STOP_PENDING)) gstop_done = task_participate_group_stop(current); - /* any trap clears pending STOP trap */ + /* any trap clears pending STOP trap, STOP trap clears NOTIFY */ task_clear_jobctl_pending(current, JOBCTL_TRAP_STOP); + if (info && info->si_code == PTRACE_STOP_SI_CODE) + task_clear_jobctl_pending(current, JOBCTL_TRAP_NOTIFY); /* entering a trap, clear TRAPPING */ task_clear_jobctl_trapping(current); @@ -1980,7 +2009,10 @@ static bool do_signal_stop(int signr) if (!task_is_stopped(t) && task_set_jobctl_pending(t, signr | gstop)) { sig->group_stop_count++; - signal_wake_up(t, 0); + if (likely(!(t->ptrace & PT_SEIZED))) + signal_wake_up(t, 0); + else + ptrace_trap_notify(t); } } } -- 1.7.5.2