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  1. 17 6月, 2011 2 次提交
    • T
      ptrace: implement PTRACE_SEIZE · 3544d72a
      由 Tejun Heo 提交于 
      PTRACE_ATTACH implicitly issues SIGSTOP on attach which has side
effects on tracee signal and job control states.  This patch
implements a new ptrace request PTRACE_SEIZE which attaches a tracee
without trapping it or affecting its signal and job control states.

The usage is the same with PTRACE_ATTACH but it takes PTRACE_SEIZE_*
flags in @data.  Currently, the only defined flag is
PTRACE_SEIZE_DEVEL which is a temporary flag to enable PTRACE_SEIZE.
PTRACE_SEIZE will change ptrace behaviors outside of attach itself.
The changes will be implemented gradually and the DEVEL flag is to
prevent programs which expect full SEIZE behavior from using it before
all the behavior modifications are complete while allowing unit
testing.  The flag will be removed once SEIZE behaviors are completely
implemented.

* PTRACE_SEIZE, unlike ATTACH, doesn't force tracee to trap.  After
  attaching tracee continues to run unless a trap condition occurs.

* PTRACE_SEIZE doesn't affect signal or group stop state.

* If PTRACE_SEIZE'd, group stop uses PTRACE_EVENT_STOP trap which uses
  exit_code of (signr | PTRACE_EVENT_STOP << 8) where signr is one of
  the stopping signals if group stop is in effect or SIGTRAP
  otherwise, and returns usual trap siginfo on PTRACE_GETSIGINFO
  instead of NULL.

Seizing sets PT_SEIZED in ->ptrace of the tracee.  This flag will be
used to determine whether new SEIZE behaviors should be enabled.

Test program follows.

  #define PTRACE_SEIZE		0x4206
  #define PTRACE_SEIZE_DEVEL	0x80000000

  static const struct timespec ts100ms = { .tv_nsec = 100000000 };
  static const struct timespec ts1s = { .tv_sec = 1 };
  static const struct timespec ts3s = { .tv_sec = 3 };

  int main(int argc, char **argv)
  {
	  pid_t tracee;

	  tracee = fork();
	  if (tracee == 0) {
		  nanosleep(&ts100ms, NULL);
		  while (1) {
			  printf("tracee: alive\n");
			  nanosleep(&ts1s, NULL);
		  }
	  }

	  if (argc > 1)
		  kill(tracee, SIGSTOP);

	  nanosleep(&ts100ms, NULL);

	  ptrace(PTRACE_SEIZE, tracee, NULL,
		 (void *)(unsigned long)PTRACE_SEIZE_DEVEL);
	  if (argc > 1) {
		  waitid(P_PID, tracee, NULL, WSTOPPED);
		  ptrace(PTRACE_CONT, tracee, NULL, NULL);
	  }
	  nanosleep(&ts3s, NULL);
	  printf("tracer: exiting\n");
	  return 0;
  }

When the above program is called w/o argument, tracee is seized while
running and remains running.  When tracer exits, tracee continues to
run and print out messages.

  # ./test-seize-simple
  tracee: alive
  tracee: alive
  tracee: alive
  tracer: exiting
  tracee: alive
  tracee: alive

When called with an argument, tracee is seized from stopped state and
continued, and returns to stopped state when tracer exits.

  # ./test-seize
  tracee: alive
  tracee: alive
  tracee: alive
  tracer: exiting
  # ps -el|grep test-seize
  1 T     0  4720     1  0  80   0 -   941 signal ttyS0    00:00:00 test-seize

-v2: SEIZE doesn't schedule TRAP_STOP and leaves tracee running as Jan
     suggested.

-v3: PTRACE_EVENT_STOP traps now report group stop state by signr.  If
     group stop is in effect the stop signal number is returned as
     part of exit_code; otherwise, SIGTRAP.  This was suggested by
     Denys and Oleg.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
      3544d72a
    • T
      job control: introduce JOBCTL_TRAP_STOP and use it for group stop trap · 73ddff2b
      由 Tejun Heo 提交于 
      do_signal_stop() implemented both normal group stop and trap for group
stop while ptraced.  This approach has been enough but scheduled
changes require trap mechanism which can be used in more generic
manner and using group stop trap for generic trap site simplifies both
userland visible interface and implementation.

This patch adds a new jobctl flag - JOBCTL_TRAP_STOP.  When set, it
triggers a trap site, which behaves like group stop trap, in
get_signal_to_deliver() after checking for pending signals.  While
ptraced, do_signal_stop() doesn't stop itself.  It initiates group
stop if requested and schedules JOBCTL_TRAP_STOP and returns.  The
caller - get_signal_to_deliver() - is responsible for checking whether
TRAP_STOP is pending afterwards and handling it.

ptrace_attach() is updated to use JOBCTL_TRAP_STOP instead of
JOBCTL_STOP_PENDING and __ptrace_unlink() to clear all pending trap
bits and TRAPPING so that TRAP_STOP and future trap bits don't linger
after detach.

While at it, add proper function comment to do_signal_stop() and make
it return bool.

-v2: __ptrace_unlink() updated to clear JOBCTL_TRAP_MASK and TRAPPING
     instead of JOBCTL_PENDING_MASK.  This avoids accidentally
     clearing JOBCTL_STOP_CONSUME.  Spotted by Oleg.

-v3: do_signal_stop() updated to return %false without dropping
     siglock while ptraced and TRAP_STOP check moved inside for(;;)
     loop after group stop participation.  This avoids unnecessary
     relocking and also will help avoiding unnecessary traps by
     consuming group stop before handling pending traps.

-v4: Jobctl trap handling moved into a separate function -
     do_jobctl_trap().
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
      73ddff2b
  3. 05 6月, 2011 9 次提交
    • T
      signal: remove three noop tracehooks · dd1d6772
      由 Tejun Heo 提交于 
      Remove the following three noop tracehooks in signals.c.

* tracehook_force_sigpending()
* tracehook_get_signal()
* tracehook_finish_jctl()

The code area is about to be updated and these hooks don't do anything
other than obfuscating the logic.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      dd1d6772
    • T
      ptrace: use bit_waitqueue for TRAPPING instead of wait_chldexit · 62c124ff
      由 Tejun Heo 提交于 
      ptracer->signal->wait_chldexit was used to wait for TRAPPING; however,
->wait_chldexit was already complicated with waker-side filtering
without adding TRAPPING wait on top of it.  Also, it unnecessarily
made TRAPPING clearing depend on the current ptrace relationship - if
the ptracee is detached, wakeup is lost.

There is no reason to use signal->wait_chldexit here.  We're just
waiting for JOBCTL_TRAPPING bit to clear and given the relatively
infrequent use of ptrace, bit_waitqueue can serve it perfectly.

This patch makes JOBCTL_TRAPPING wait use bit_waitqueue instead of
signal->wait_chldexit.

-v2: Use JOBCTL_*_BIT macros instead of ilog2() as suggested by Linus.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      62c124ff
    • T
      job control: introduce task_set_jobctl_pending() · 7dd3db54
      由 Tejun Heo 提交于 
      task->jobctl currently hosts JOBCTL_STOP_PENDING and will host TRAP
pending bits too.  Setting pending conditions on a dying task may make
the task unkillable.  Currently, each setting site is responsible for
checking for the condition but with to-be-added job control traps this
becomes too fragile.

This patch adds task_set_jobctl_pending() which should be used when
setting task->jobctl bits to schedule a stop or trap.  The function
performs the followings to ease setting pending bits.

* Sanity checks.

* If fatal signal is pending or PF_EXITING is set, no bit is set.

* STOP_SIGMASK is automatically cleared if new value is being set.

do_signal_stop() and ptrace_attach() are updated to use
task_set_jobctl_pending() instead of setting STOP_PENDING explicitly.
The surrounding structures around setting are changed to fit
task_set_jobctl_pending() better but there should be no userland
visible behavior difference.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      7dd3db54
    • T
      job control: make task_clear_jobctl_pending() clear TRAPPING automatically · 6dfca329
      由 Tejun Heo 提交于 
      JOBCTL_TRAPPING indicates that ptracer is waiting for tracee to
(re)transit into TRACED.  task_clear_jobctl_pending() must be called
when either tracee enters TRACED or the transition is cancelled for
some reason.  The former is achieved by explicitly calling
task_clear_jobctl_pending() in ptrace_stop() and the latter by calling
it at the end of do_signal_stop().

Calling task_clear_jobctl_trapping() at the end of do_signal_stop()
limits the scope TRAPPING can be used and is fragile in that seemingly
unrelated changes to tracee's control flow can lead to stuck TRAPPING.

We already have task_clear_jobctl_pending() calls on those cancelling
events to clear JOBCTL_STOP_PENDING.  Cancellations can be handled by
making those call sites use JOBCTL_PENDING_MASK instead and updating
task_clear_jobctl_pending() such that task_clear_jobctl_trapping() is
called automatically if no stop/trap is pending.

This patch makes the above changes and removes the fallback
task_clear_jobctl_trapping() call from do_signal_stop().
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      6dfca329
    • T
      job control: introduce JOBCTL_PENDING_MASK and task_clear_jobctl_pending() · 3759a0d9
      由 Tejun Heo 提交于 
      This patch introduces JOBCTL_PENDING_MASK and replaces
task_clear_jobctl_stop_pending() with task_clear_jobctl_pending()
which takes an extra @mask argument.

JOBCTL_PENDING_MASK is currently equal to JOBCTL_STOP_PENDING but
future patches will add more bits.  recalc_sigpending_tsk() is updated
to use JOBCTL_PENDING_MASK instead.

task_clear_jobctl_pending() takes @mask which in subset of
JOBCTL_PENDING_MASK and clears the relevant jobctl bits.  If
JOBCTL_STOP_PENDING is set, other STOP bits are cleared together.  All
task_clear_jobctl_stop_pending() users are updated to call
task_clear_jobctl_pending() with JOBCTL_STOP_PENDING which is
functionally identical to task_clear_jobctl_stop_pending().

This patch doesn't cause any functional change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      3759a0d9
    • T
      ptrace: relocate set_current_state(TASK_TRACED) in ptrace_stop() · 81be24b8
      由 Tejun Heo 提交于 
      In ptrace_stop(), after arch hook is done, the task state and jobctl
bits are updated while holding siglock.  The ordering requirement
there is that TASK_TRACED is set before JOBCTL_TRAPPING is cleared to
prevent ptracer waiting on TRAPPING doesn't end up waking up TRACED is
actually set and sees TASK_RUNNING in wait(2).

Move set_current_state(TASK_TRACED) to the top of the block and
reorganize comments.  This makes the ordering more obvious
(TASK_TRACED before other updates) and helps future updates to group
stop participation.

This patch doesn't cause any functional change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      81be24b8
    • T
      ptrace: ptrace_check_attach(): rename @kill to @ignore_state and add comments · 755e276b
      由 Tejun Heo 提交于 
      PTRACE_INTERRUPT is going to be added which should also skip
task_is_traced() check in ptrace_check_attach().  Rename @kill to
@ignore_state and make it bool.  Add function comment while at it.

This patch doesn't introduce any behavior difference.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      755e276b
    • T
      job control: rename signal->group_stop and flags to jobctl and update them · a8f072c1
      由 Tejun Heo 提交于 
      signal->group_stop currently hosts mostly group stop related flags;
however, it's gonna be used for wider purposes and the GROUP_STOP_
flag prefix becomes confusing.  Rename signal->group_stop to
signal->jobctl and rename all GROUP_STOP_* flags to JOBCTL_*.

Bit position macros JOBCTL_*_BIT are defined and JOBCTL_* flags are
defined in terms of them to allow using bitops later.

While at it, reassign JOBCTL_TRAPPING to bit 22 to better accomodate
future additions.

This doesn't cause any functional change.

-v2: JOBCTL_*_BIT macros added as suggested by Linus.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      a8f072c1
    • T
      ptrace: remove silly wait_trap variable from ptrace_attach() · 0b1007c3
      由 Tejun Heo 提交于 
      Remove local variable wait_trap which determines whether to wait for
!TRAPPING or not and simply wait for it if attach was successful.

-v2: Oleg pointed out wait should happen iff attach was successful.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      0b1007c3
  5. 04 6月, 2011 12 次提交
  7. 03 6月, 2011 10 次提交
  9. 02 6月, 2011 7 次提交