[patch] Fix for PR gdb/10757
Paul Pluzhnikov
ppluzhnikov@google.com
Thu Oct 15 19:10:00 GMT 2009
Greetings,
Here is a proposed fix for gdb/10757:
http://sourceware.org/bugzilla/show_bug.cgi?id=10757
It appears to me that the Linux thread_db interface is horribly broken,
especially this part:
+ This could mean that the thread list inside glibc itself is in
+ inconsistent state, and libthread_db could go on looping forever
+ (observed with glibc-2.3.6). To prevent that, terminate
+ iteration: thread_db_find_new_threads_2 will retry. */
+ return 1;
Tested on Linux/x86_64.
[gdbserver will need similar fixes.]
Thanks,
--
Paul Pluzhnikov
2009-10-15 Paul Pluzhnikov <ppluzhnikov@google.com>
PR gdb/10757
* linux-thread-db.c (attach_thread): Return success/failure
indicator.
(thread_db_find_new_threads_silently): Retry until no new threads.
(struct callback_data): New.
(find_new_threads_callback): Count new threads, stop iteration
on error.
(find_new_threads_once): New function.
(thread_db_find_new_threads_2): Rename from
thread_db_find_new_threads_1 and adjust.
(thread_db_find_new_threads_1): New function.
Index: linux-thread-db.c
===================================================================
RCS file: /cvs/src/src/gdb/linux-thread-db.c,v
retrieving revision 1.64
diff -u -p -u -r1.64 linux-thread-db.c
--- linux-thread-db.c 16 Jul 2009 20:45:17 -0000 1.64
+++ linux-thread-db.c 15 Oct 2009 18:55:28 -0000
@@ -160,6 +160,7 @@ struct thread_db_info
struct thread_db_info *thread_db_list;
static void thread_db_find_new_threads_1 (ptid_t ptid);
+static void thread_db_find_new_threads_2 (ptid_t ptid, int num_loop);
/* Add the current inferior to the list of processes using libpthread.
Return a pointer to the newly allocated object that was added to
@@ -229,8 +230,8 @@ delete_thread_db_info (int pid)
}
/* Prototypes for local functions. */
-static void attach_thread (ptid_t ptid, const td_thrhandle_t *th_p,
- const td_thrinfo_t *ti_p);
+static int attach_thread (ptid_t ptid, const td_thrhandle_t *th_p,
+ const td_thrinfo_t *ti_p);
static void detach_thread (ptid_t ptid);
@@ -597,7 +598,7 @@ thread_db_find_new_threads_silently (pti
TRY_CATCH (except, RETURN_MASK_ERROR)
{
- thread_db_find_new_threads_1 (ptid);
+ thread_db_find_new_threads_2 (ptid, 4);
}
if (except.reason < 0 && info_verbose)
@@ -977,9 +978,9 @@ thread_db_new_objfile (struct objfile *o
/* Attach to a new thread. This function is called when we receive a
TD_CREATE event or when we iterate over all threads and find one
- that wasn't already in our list. */
+ that wasn't already in our list. Returns true on success. */
-static void
+static int
attach_thread (ptid_t ptid, const td_thrhandle_t *th_p,
const td_thrinfo_t *ti_p)
{
@@ -1013,7 +1014,7 @@ attach_thread (ptid_t ptid, const td_thr
if (tp->private != NULL)
{
if (!tp->private->dying)
- return;
+ return 0;
delete_thread (ptid);
tp = NULL;
@@ -1023,12 +1024,12 @@ attach_thread (ptid_t ptid, const td_thr
check_thread_signals ();
if (ti_p->ti_state == TD_THR_UNKNOWN || ti_p->ti_state == TD_THR_ZOMBIE)
- return; /* A zombie thread -- do not attach. */
+ return 0; /* A zombie thread -- do not attach. */
/* Under GNU/Linux, we have to attach to each and every thread. */
if (tp == NULL
&& lin_lwp_attach_lwp (BUILD_LWP (ti_p->ti_lid, GET_PID (ptid))) < 0)
- return;
+ return 0;
/* Construct the thread's private data. */
private = xmalloc (sizeof (struct private_thread_info));
@@ -1056,6 +1057,7 @@ attach_thread (ptid_t ptid, const td_thr
if (err != TD_OK)
error (_("Cannot enable thread event reporting for %s: %s"),
target_pid_to_str (ptid), thread_db_err_str (err));
+ return 1;
}
static void
@@ -1286,6 +1288,12 @@ thread_db_mourn_inferior (struct target_
unpush_target (ops);
}
+struct callback_data
+{
+ struct thread_db_info *info;
+ int new_threads;
+};
+
static int
find_new_threads_callback (const td_thrhandle_t *th_p, void *data)
{
@@ -1293,7 +1301,8 @@ find_new_threads_callback (const td_thrh
td_err_e err;
ptid_t ptid;
struct thread_info *tp;
- struct thread_db_info *info = data;
+ struct callback_data *cb_data = data;
+ struct thread_db_info *info = cb_data->info;
err = info->td_thr_get_info_p (th_p, &ti);
if (err != TD_OK)
@@ -1336,21 +1345,76 @@ find_new_threads_callback (const td_thrh
ptid = ptid_build (info->pid, ti.ti_lid, 0);
tp = find_thread_ptid (ptid);
if (tp == NULL || tp->private == NULL)
- attach_thread (ptid, th_p, &ti);
+ {
+ if (attach_thread (ptid, th_p, &ti))
+ cb_data->new_threads += 1;
+ else
+ /* Problem attaching this thread; perhaps it exited before we
+ could attach it?
+ This could mean that the thread list inside glibc itself is in
+ inconsistent state, and libthread_db could go on looping forever
+ (observed with glibc-2.3.6). To prevent that, terminate
+ iteration: thread_db_find_new_threads_2 will retry. */
+ return 1;
+ }
return 0;
}
+/* Helper for thread_db_find_new_threads_2.
+ Returns number of new threads found. */
+
+static int
+find_new_threads_once (struct thread_db_info *info, int iteration,
+ int *errp)
+{
+ volatile struct gdb_exception except;
+ struct callback_data data;
+ int err;
+
+ data.info = info;
+ data.new_threads = 0;
+
+ TRY_CATCH (except, RETURN_MASK_ERROR)
+ {
+ /* Iterate over all user-space threads to discover new threads. */
+ err = info->td_ta_thr_iter_p (info->thread_agent,
+ find_new_threads_callback,
+ &data,
+ TD_THR_ANY_STATE,
+ TD_THR_LOWEST_PRIORITY,
+ TD_SIGNO_MASK,
+ TD_THR_ANY_USER_FLAGS);
+ }
+
+ if (info_verbose)
+ {
+ if (except.reason < 0)
+ exception_fprintf (gdb_stderr, except,
+ "Warning: find_new_threads_once: ");
+
+ printf_filtered (_("Found %d new threads in iteration %d.\n"),
+ data.new_threads, iteration);
+ }
+
+ if (errp != NULL)
+ *errp = err;
+
+ return data.new_threads;
+}
+
/* Search for new threads, accessing memory through stopped thread
- PTID. */
+ PTID. If NUM_LOOPS is non-zero, repeat searching until NUM_LOOP
+ searches in a row do not discover any new threads. */
static void
-thread_db_find_new_threads_1 (ptid_t ptid)
+thread_db_find_new_threads_2 (ptid_t ptid, int num_loop)
{
td_err_e err;
struct lwp_info *lp;
struct thread_db_info *info;
int pid = ptid_get_pid (ptid);
+ int i, loop;
/* In linux, we can only read memory through a stopped lwp. */
ALL_LWPS (lp, ptid)
@@ -1365,15 +1429,33 @@ thread_db_find_new_threads_1 (ptid_t pti
/* Access an lwp we know is stopped. */
info->proc_handle.ptid = ptid;
- /* Iterate over all user-space threads to discover new threads. */
- err = info->td_ta_thr_iter_p (info->thread_agent, find_new_threads_callback,
- info, TD_THR_ANY_STATE, TD_THR_LOWEST_PRIORITY,
- TD_SIGNO_MASK, TD_THR_ANY_USER_FLAGS);
- if (err != TD_OK)
- error (_("Cannot find new threads: %s"), thread_db_err_str (err));
+
+ if (num_loop != 0)
+ {
+ /* Require NUM_LOOP successive iterations which do not find any new threads. */
+ for (i = 0, loop = 0; loop < 4; ++i, ++loop)
+ if (find_new_threads_once (info, i, NULL) != 0)
+ /* Found some new threads. Restart the loop from beginning. */
+ loop = -1;
+ }
+ else
+ {
+ int err;
+
+ find_new_threads_once (info, 0, &err);
+ if (err != TD_OK)
+ error (_("Cannot find new threads: %s"), thread_db_err_str (err));
+ }
}
static void
+thread_db_find_new_threads_1 (ptid_t ptid)
+{
+ thread_db_find_new_threads_2 (ptid, 0);
+}
+
+
+static void
thread_db_find_new_threads (struct target_ops *ops)
{
struct thread_db_info *info;
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