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PR gdb/15713 - errors from i386_linux_resume lead to lock-up 

linux_nat_resume is not considering that linux_ops->to_resume may throw:

  /* Mark LWP as not stopped to prevent it from being continued by
     linux_nat_resume_callback.  */
  lp->stopped = 0;

  if (resume_many)
    iterate_over_lwps (ptid, linux_nat_resume_callback, NULL);

If something within linux_nat_resume_callback throws, GDB leaves the
lwp_info as if the inferior was resumed, while it actually wasn't.

A couple examples, there are possibly others:

 - i386_linux_resume calls target_read which calls QUIT.
 - if the actual ptrace resumption fails in inf_ptrace_resume,
   perror_with_name is called.

If the user tries to kill the inferior at this point (or quit, which
offers to kill), GDB locks up trying to stop the lwp -- if it is
already stopped no new waitpid event gets generated for it.

Fix this by setting the stopped flag earlier, as soon as we collect a
stop event with waitpid, and clearing it always only after resuming
the lwp successfully.

Tested on x86_64 Fedora 20.  Confirmed the lock-up disappears using a
local hack that forces an error in inf_ptrace_resume.

Also fixes a little "set debug lin-lwp" annoyance.  Currently we always see:

 Continuing.
 LLR: Preparing to resume process 6802, 0, inferior_ptid Thread 0x7ffff7fc7740 (LWP 6802)
                                                                                ^^^^^^^^
 RC: Resuming sibling Thread 0x7ffff77c5700 (LWP 6807), 0, resume
 RC: Resuming sibling Thread 0x7ffff7fc6700 (LWP 6806), 0, resume
 RC: Not resuming sibling Thread 0x7ffff7fc7740 (LWP 6802) (not stopped)
                                                 ^^^^^^^^^^^^^^^^^^^^^^^
 LLR: PTRACE_CONT process 6802, 0 (resume event thread)

This patch gets rid of the "Not resuming sibling" line.

2014-05-29  Pedro Alves  <palves@redhat.com>

	PR gdb/15713
	* linux-nat.c (linux_nat_resume_callback): Rename the second
	parameter to 'except'.  Skip LP if it points to EXCEPT.
	(linux_nat_resume): Don't mark the event lwp as not stopped
	before resuming sibling lwps.  Instead ask
	linux_nat_resume_callback to skip the event lwp.  Mark it as not
	stopped after actually resuming it.
	(linux_handle_syscall_trap): Mark the lwp as not stopped after
	resuming it.
	(wait_lwp): Mark the lwp as stopped here.
	(stop_wait_callback): Mark the lwp as not stopped right after
	resuming it.  Don't mark lwps as stopped here.
	(linux_nat_filter_event): Mark the lwp as stopped earlier.
	(linux_nat_wait_1): Don't mark dead lwps as stopped here.
This commit is contained in:
Pedro Alves 2014-05-29 12:50:48 +01:00
parent 251bde03ba
commit 8817a6f225
2 changed files with 35 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
gdb/ChangeLog
View File

@ -1,3 +1,20 @@
2014-05-29 Pedro Alves <palves@redhat.com>
PR gdb/15713
* linux-nat.c (linux_nat_resume_callback): Rename the second
parameter to 'except'. Skip LP if it points to EXCEPT.
(linux_nat_resume): Don't mark the event lwp as not stopped
before resuming sibling lwps. Instead ask
linux_nat_resume_callback to skip the event lwp. Mark it as not
stopped after actually resuming it.
(linux_handle_syscall_trap): Mark the lwp as not stopped after
resuming it.
(wait_lwp): Mark the lwp as stopped here.
(stop_wait_callback): Mark the lwp as not stopped right after
resuming it. Don't mark lwps as stopped here.
(linux_nat_filter_event): Mark the lwp as stopped earlier.
(linux_nat_wait_1): Don't mark dead lwps as stopped here.
2014-05-29 Pedro Alves <palves@redhat.com>
PR PR15693

41
gdb/linux-nat.c
View File

@ -1647,13 +1647,17 @@ resume_lwp (struct lwp_info *lp, int step, enum gdb_signal signo)
}
}
/* Resume LWP, with the last stop signal, if it is in pass state. */
/* Callback for iterate_over_lwps. If LWP is EXCEPT, do nothing.
Resume LWP with the last stop signal, if it is in pass state. */
static int
linux_nat_resume_callback (struct lwp_info *lp, void *data)
linux_nat_resume_callback (struct lwp_info *lp, void *except)
{
enum gdb_signal signo = GDB_SIGNAL_0;
if (lp == except)
return 0;
if (lp->stopped)
{
struct thread_info *thread;
@ -1769,12 +1773,8 @@ linux_nat_resume (struct target_ops *ops,
return;
}
/* Mark LWP as not stopped to prevent it from being continued by
linux_nat_resume_callback. */
lp->stopped = 0;
if (resume_many)
iterate_over_lwps (ptid, linux_nat_resume_callback, NULL);
iterate_over_lwps (ptid, linux_nat_resume_callback, lp);
/* Convert to something the lower layer understands. */
ptid = pid_to_ptid (ptid_get_lwp (lp->ptid));
@ -1783,6 +1783,7 @@ linux_nat_resume (struct target_ops *ops,
linux_nat_prepare_to_resume (lp);
linux_ops->to_resume (linux_ops, ptid, step, signo);
lp->stopped_by_watchpoint = 0;
lp->stopped = 0;
if (debug_linux_nat)
fprintf_unfiltered (gdb_stdlog,
@ -1869,6 +1870,7 @@ linux_handle_syscall_trap (struct lwp_info *lp, int stopping)
lp->syscall_state = TARGET_WAITKIND_IGNORE;
ptrace (PTRACE_CONT, ptid_get_lwp (lp->ptid), 0, 0);
lp->stopped = 0;
return 1;
}
@ -1952,6 +1954,7 @@ linux_handle_syscall_trap (struct lwp_info *lp, int stopping)
linux_nat_prepare_to_resume (lp);
linux_ops->to_resume (linux_ops, pid_to_ptid (ptid_get_lwp (lp->ptid)),
lp->step, GDB_SIGNAL_0);
lp->stopped = 0;
return 1;
}
@ -2161,7 +2164,7 @@ linux_handle_extended_wait (struct lwp_info *lp, int status,
linux_ops->to_resume (linux_ops,
pid_to_ptid (ptid_get_lwp (lp->ptid)),
0, GDB_SIGNAL_0);
lp->stopped = 0;
return 1;
}
@ -2316,6 +2319,7 @@ wait_lwp (struct lwp_info *lp)
}
gdb_assert (WIFSTOPPED (status));
lp->stopped = 1;
/* Handle GNU/Linux's syscall SIGTRAPs. */
if (WIFSTOPPED (status) && WSTOPSIG (status) == SYSCALL_SIGTRAP)
@ -2569,6 +2573,7 @@ stop_wait_callback (struct lwp_info *lp, void *data)
errno = 0;
ptrace (PTRACE_CONT, ptid_get_lwp (lp->ptid), 0, 0);
lp->stopped = 0;
if (debug_linux_nat)
fprintf_unfiltered (gdb_stdlog,
"PTRACE_CONT %s, 0, 0 (%s) "
@ -2595,9 +2600,7 @@ stop_wait_callback (struct lwp_info *lp, void *data)
/* Save the sigtrap event. */
lp->status = status;
gdb_assert (!lp->stopped);
gdb_assert (lp->signalled);
lp->stopped = 1;
}
else
{
@ -2609,8 +2612,6 @@ stop_wait_callback (struct lwp_info *lp, void *data)
"SWC: Delayed SIGSTOP caught for %s.\n",
target_pid_to_str (lp->ptid));
lp->stopped = 1;
/* Reset SIGNALLED only after the stop_wait_callback call
above as it does gdb_assert on SIGNALLED. */
lp->signalled = 0;
@ -2938,6 +2939,10 @@ linux_nat_filter_event (int lwpid, int status, int *new_pending_p)
if (!WIFSTOPPED (status) && !lp)
return NULL;
/* This LWP is stopped now. (And if dead, this prevents it from
ever being continued.) */
lp->stopped = 1;
/* Handle GNU/Linux's syscall SIGTRAPs. */
if (WIFSTOPPED (status) && WSTOPSIG (status) == SYSCALL_SIGTRAP)
{
@ -2980,7 +2985,6 @@ linux_nat_filter_event (int lwpid, int status, int *new_pending_p)
used. */
if (ptid_get_pid (lp->ptid) == ptid_get_lwp (lp->ptid))
{
lp->stopped = 1;
iterate_over_lwps (pid_to_ptid (ptid_get_pid (lp->ptid)),
stop_and_resume_callback, new_pending_p);
}
@ -3325,13 +3329,9 @@ retry:
" cancelled it\n",
ptid_get_lwp (lp->ptid));
}
lp->stopped = 1;
}
else
{
lp->stopped = 1;
lp->signalled = 0;
}
lp->signalled = 0;
}
else if (WIFEXITED (lp->status) || WIFSIGNALED (lp->status))
{
@ -3348,11 +3348,6 @@ retry:
pending for the next time we're able to report
it. */
/* Prevent trying to stop this thread again. We'll
never try to resume it because it has a pending
status. */
lp->stopped = 1;
/* Dead LWP's aren't expected to reported a pending
sigstop. */
lp->signalled = 0;