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Don't delete thread_info if refcount isn't zero
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I build GDB with asan, and run test case hook-stop.exp, and threadapply.exp,
I got the following asan error,

=================================================================^M
^[[1m^[[31m==2291==ERROR: AddressSanitizer: heap-use-after-free on address 0x6160000999c4 at pc 0x000000826022 bp 0x7ffd28a8ff70 sp 0x7ffd28a8ff60^M
^[[1m^[[0m^[[1m^[[34mREAD of size 4 at 0x6160000999c4 thread T0^[[1m^[[0m^M
    #0 0x826021 in release_stop_context_cleanup ../../binutils-gdb/gdb/infrun.c:8203^M
    #1 0x72798a in do_my_cleanups ../../binutils-gdb/gdb/common/cleanups.c:154^M
    #2 0x727a32 in do_cleanups(cleanup*) ../../binutils-gdb/gdb/common/cleanups.c:176^M
    #3 0x826895 in normal_stop() ../../binutils-gdb/gdb/infrun.c:8381^M
    #4 0x815208 in fetch_inferior_event(void*) ../../binutils-gdb/gdb/infrun.c:4011^M
    #5 0x868aca in inferior_event_handler(inferior_event_type, void*) ../../binutils-gdb/gdb/inf-loop.c:44^M
....
^[[1m^[[32m0x6160000999c4 is located 68 bytes inside of 568-byte region [0x616000099980,0x616000099bb8)^M
^[[1m^[[0m^[[1m^[[35mfreed by thread T0 here:^[[1m^[[0m^M
    #0 0x7fb0bc1312ca in __interceptor_free (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x982ca)^M
    #1 0xb8c62f in xfree(void*) ../../binutils-gdb/gdb/common/common-utils.c:100^M
    #2 0x83df67 in free_thread ../../binutils-gdb/gdb/thread.c:207^M
    #3 0x83dfd2 in init_thread_list() ../../binutils-gdb/gdb/thread.c:223^M
    #4 0x805494 in kill_command ../../binutils-gdb/gdb/infcmd.c:2595^M
....

Detaching from program: /home/yao.qi/SourceCode/gnu/build-with-asan/gdb/testsuite/outputs/gdb.threads/threadapply/threadapply, process 2399^M
=================================================================^M
^[[1m^[[31m==2387==ERROR: AddressSanitizer: heap-use-after-free on address 0x6160000a98c0 at pc 0x00000083fd28 bp 0x7ffd401c3110 sp 0x7ffd401c3100^M
^[[1m^[[0m^[[1m^[[34mREAD of size 4 at 0x6160000a98c0 thread T0^[[1m^[[0m^M
    #0 0x83fd27 in thread_alive ../../binutils-gdb/gdb/thread.c:741^M
    #1 0x844277 in thread_apply_all_command ../../binutils-gdb/gdb/thread.c:1804^M
....
^M
^[[1m^[[32m0x6160000a98c0 is located 64 bytes inside of 568-byte region [0x6160000a9880,0x6160000a9ab8)^M
^[[1m^[[0m^[[1m^[[35mfreed by thread T0 here:^[[1m^[[0m^M
    #0 0x7f59a7e322ca in __interceptor_free (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x982ca)^M
    #1 0xb8c62f in xfree(void*) ../../binutils-gdb/gdb/common/common-utils.c:100^M
    #2 0x83df67 in free_thread ../../binutils-gdb/gdb/thread.c:207^M
    #3 0x83dfd2 in init_thread_list() ../../binutils-gdb/gdb/thread.c:223^M

This patch fixes the issue by deleting thread_info object if it is
deletable, otherwise, mark it as exited (by set_thread_exited).
Function set_thread_exited is shared from delete_thread_1.  This patch
also moves field "refcount" to private and methods incref and
decref.  Additionally, we stop using "ptid_t" in
"struct current_thread_cleanup" to reference threads, instead we use
"thread_info" directly.  Due to this change, we don't need
restore_current_thread_ptid_changed anymore.

gdb:

2017-04-10  Yao Qi  <[email protected]>

	PR gdb/19942
	* gdbthread.h (thread_info::deletable): New method.
	(thread_info::incref): New method.
	(thread_info::decref): New method.
	(thread_info::refcount): Move it to private.
	* infrun.c (save_stop_context): Call inc_refcount.
	(release_stop_context_cleanup): Likewise.
	* thread.c (set_thread_exited): New function.
	(init_thread_list): Delete "tp" only it is deletable, otherwise
	call set_thread_exited.
	(delete_thread_1): Call set_thread_exited.
	(current_thread_cleanup) <inferior_pid>: Remove.
	<thread>: New field.
	(restore_current_thread_ptid_changed): Removed.
	(do_restore_current_thread_cleanup): Adjust.
	(restore_current_thread_cleanup_dtor): Don't call
	find_thread_ptid.
	(set_thread_refcount): Use dec_refcount.
	(make_cleanup_restore_current_thread): Adjust.
	(thread_apply_all_command): Call inc_refcount.
	(_initialize_thread): Don't call
	observer_attach_thread_ptid_changed.
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Yao Qi committed Apr 10, 2017
1 parent 8c25b49 commit 803bdfe
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Showing 4 changed files with 101 additions and 62 deletions.
25 changes: 25 additions & 0 deletions gdb/ChangeLog
View file
Original file line number Diff line number Diff line change
@@ -1,3 +1,28 @@
2017-04-10 Yao Qi <[email protected]>

PR gdb/19942
* gdbthread.h (thread_info::deletable): New method.
(thread_info::incref): New method.
(thread_info::decref): New method.
(thread_info::refcount): Move it to private.
* infrun.c (save_stop_context): Call inc_refcount.
(release_stop_context_cleanup): Likewise.
* thread.c (set_thread_exited): New function.
(init_thread_list): Delete "tp" only it is deletable, otherwise
call set_thread_exited.
(delete_thread_1): Call set_thread_exited.
(current_thread_cleanup) <inferior_pid>: Remove.
<thread>: New field.
(restore_current_thread_ptid_changed): Removed.
(do_restore_current_thread_cleanup): Adjust.
(restore_current_thread_cleanup_dtor): Don't call
find_thread_ptid.
(set_thread_refcount): Use dec_refcount.
(make_cleanup_restore_current_thread): Adjust.
(thread_apply_all_command): Call inc_refcount.
(_initialize_thread): Don't call
observer_attach_thread_ptid_changed.

2017-04-10 Yao Qi <[email protected]>

* thread.c (delete_thread_1): Hoist code on marking thread as
Expand Down
33 changes: 28 additions & 5 deletions gdb/gdbthread.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,27 @@ struct thread_info
explicit thread_info (inferior *inf, ptid_t ptid);
~thread_info ();

bool deletable () const
{
/* If this is the current thread, or there's code out there that
relies on it existing (m_refcount > 0) we can't delete yet. */
return (m_refcount == 0 && !ptid_equal (ptid, inferior_ptid));
}

/* Increase the refcount. */
void incref ()
{
gdb_assert (m_refcount >= 0);
m_refcount++;
}

/* Decrease the refcount. */
void decref ()
{
m_refcount--;
gdb_assert (m_refcount >= 0);
}

struct thread_info *next = NULL;
ptid_t ptid; /* "Actual process id";
In fact, this may be overloaded with
Expand Down Expand Up @@ -254,11 +275,6 @@ struct thread_info
but STATE will still be THREAD_RUNNING. */
enum thread_state state = THREAD_STOPPED;

/* If this is > 0, then it means there's code out there that relies
on this thread being listed. Don't delete it from the lists even
if we detect it exiting. */
int refcount = 0;

/* State of GDB control of inferior thread execution.
See `struct thread_control_state'. */
thread_control_state control {};
Expand Down Expand Up @@ -346,6 +362,13 @@ struct thread_info
fields point to self. */
struct thread_info *step_over_prev = NULL;
struct thread_info *step_over_next = NULL;

private:

/* If this is > 0, then it means there's code out there that relies
on this thread being listed. Don't delete it from the lists even
if we detect it exiting. */
int m_refcount = 0;
};

/* Create an empty thread list, or empty the existing one. */
Expand Down
4 changes: 2 additions & 2 deletions gdb/infrun.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -8165,7 +8165,7 @@ save_stop_context (void)
/* Take a strong reference so that the thread can't be deleted
yet. */
sc->thread = inferior_thread ();
sc->thread->refcount++;
sc->thread->incref ();
}
else
sc->thread = NULL;
Expand All @@ -8182,7 +8182,7 @@ release_stop_context_cleanup (void *arg)
struct stop_context *sc = (struct stop_context *) arg;

if (sc->thread != NULL)
sc->thread->refcount--;
sc->thread->decref ();
xfree (sc);
}

Expand Down
101 changes: 46 additions & 55 deletions gdb/thread.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -192,6 +192,27 @@ clear_thread_inferior_resources (struct thread_info *tp)
thread_cancel_execution_command (tp);
}

/* Set the TP's state as exited. */

static void
set_thread_exited (thread_info *tp, int silent)
{
/* Dead threads don't need to step-over. Remove from queue. */
if (tp->step_over_next != NULL)
thread_step_over_chain_remove (tp);

if (tp->state != THREAD_EXITED)
{
observer_notify_thread_exit (tp, silent);

/* Tag it as exited. */
tp->state = THREAD_EXITED;

/* Clear breakpoints, etc. associated with this thread. */
clear_thread_inferior_resources (tp);
}
}

void
init_thread_list (void)
{
Expand All @@ -205,7 +226,10 @@ init_thread_list (void)
for (tp = thread_list; tp; tp = tpnext)
{
tpnext = tp->next;
delete tp;
if (tp->deletable ())
delete tp;
else
set_thread_exited (tp, 1);
}

thread_list = NULL;
Expand Down Expand Up @@ -430,25 +454,9 @@ delete_thread_1 (ptid_t ptid, int silent)
if (!tp)
return;

/* Dead threads don't need to step-over. Remove from queue. */
if (tp->step_over_next != NULL)
thread_step_over_chain_remove (tp);
set_thread_exited (tp, silent);

if (tp->state != THREAD_EXITED)
{
observer_notify_thread_exit (tp, silent);

/* Tag it as exited. */
tp->state = THREAD_EXITED;

/* Clear breakpoints, etc. associated with this thread. */
clear_thread_inferior_resources (tp);
}

/* If this is the current thread, or there's code out there that
relies on it existing (refcount > 0) we can't delete yet. */
if (tp->refcount > 0
|| ptid_equal (tp->ptid, inferior_ptid))
if (!tp->deletable ())
{
/* Will be really deleted some other time. */
return;
Expand Down Expand Up @@ -1546,7 +1554,7 @@ struct current_thread_cleanup
'current_thread_cleanup_chain' below. */
struct current_thread_cleanup *next;

ptid_t inferior_ptid;
thread_info *thread;
struct frame_id selected_frame_id;
int selected_frame_level;
int was_stopped;
Expand All @@ -1561,37 +1569,21 @@ struct current_thread_cleanup
succeeds. */
static struct current_thread_cleanup *current_thread_cleanup_chain;

/* A thread_ptid_changed observer. Update all currently installed
current_thread_cleanup cleanups that want to switch back to
OLD_PTID to switch back to NEW_PTID instead. */

static void
restore_current_thread_ptid_changed (ptid_t old_ptid, ptid_t new_ptid)
{
struct current_thread_cleanup *it;

for (it = current_thread_cleanup_chain; it != NULL; it = it->next)
{
if (ptid_equal (it->inferior_ptid, old_ptid))
it->inferior_ptid = new_ptid;
}
}

static void
do_restore_current_thread_cleanup (void *arg)
{
struct thread_info *tp;
struct current_thread_cleanup *old = (struct current_thread_cleanup *) arg;

tp = find_thread_ptid (old->inferior_ptid);

/* If the previously selected thread belonged to a process that has
in the mean time been deleted (due to normal exit, detach, etc.),
then don't revert back to it, but instead simply drop back to no
thread selected. */
if (tp
&& find_inferior_ptid (tp->ptid) != NULL)
restore_current_thread (old->inferior_ptid);
/* If an entry of thread_info was previously selected, it won't be
deleted because we've increased its refcount. The thread represented
by this thread_info entry may have already exited (due to normal exit,
detach, etc), so the thread_info.state is THREAD_EXITED. */
if (old->thread != NULL
/* If the previously selected thread belonged to a process that has
in the mean time exited (or killed, detached, etc.), then don't revert
back to it, but instead simply drop back to no thread selected. */
&& find_inferior_ptid (old->thread->ptid) != NULL)
restore_current_thread (old->thread->ptid);
else
{
restore_current_thread (null_ptid);
Expand Down Expand Up @@ -1619,9 +1611,9 @@ restore_current_thread_cleanup_dtor (void *arg)

current_thread_cleanup_chain = current_thread_cleanup_chain->next;

tp = find_thread_ptid (old->inferior_ptid);
if (tp)
tp->refcount--;
if (old->thread != NULL)
old->thread->decref ();

inf = find_inferior_id (old->inf_id);
if (inf != NULL)
inf->removable = old->was_removable;
Expand All @@ -1638,15 +1630,15 @@ set_thread_refcount (void *data)
= (struct thread_array_cleanup *) data;

for (k = 0; k != ta_cleanup->count; k++)
ta_cleanup->tp_array[k]->refcount--;
ta_cleanup->tp_array[k]->decref ();
}

struct cleanup *
make_cleanup_restore_current_thread (void)
{
struct current_thread_cleanup *old = XNEW (struct current_thread_cleanup);

old->inferior_ptid = inferior_ptid;
old->thread = NULL;
old->inf_id = current_inferior ()->num;
old->was_removable = current_inferior ()->removable;

Expand Down Expand Up @@ -1679,7 +1671,8 @@ make_cleanup_restore_current_thread (void)
struct thread_info *tp = find_thread_ptid (inferior_ptid);

if (tp)
tp->refcount++;
tp->incref ();
old->thread = tp;
}

current_inferior ()->removable = 0;
Expand Down Expand Up @@ -1796,7 +1789,7 @@ thread_apply_all_command (char *cmd, int from_tty)
ALL_NON_EXITED_THREADS (tp)
{
tp_array[i] = tp;
tp->refcount++;
tp->incref ();
i++;
}
/* Because we skipped exited threads, we may end up with fewer
Expand Down Expand Up @@ -2286,6 +2279,4 @@ Show printing of thread events (such as thread start and exit)."), NULL,

create_internalvar_type_lazy ("_thread", &thread_funcs, NULL);
create_internalvar_type_lazy ("_gthread", &gthread_funcs, NULL);

observer_attach_thread_ptid_changed (restore_current_thread_ptid_changed);
}

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