[binutils-gdb] gdbserver resume_stop handling bug

[Pedro Alves <palves at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=56cf4bed5354769d7352c5cf4e054a346d2553cd

commit 56cf4bed5354769d7352c5cf4e054a346d2553cd
Author: Pedro Alves <palves@redhat.com>
Date:   Mon Nov 30 16:05:19 2015 +0000

    gdbserver resume_stop handling bug
    
    Running attach-many-short-lived-threads.exp with the extended-remote
    board with "maint set target-non-stop on" times out -- the attach
    never completes.  Enabling infrun debug logs, we see that GDB is stuck
    stopping all threads:
    
     infrun: target_wait (-1.0.0, status) =
     infrun:   1639.22213.0 [Thread 1639.22213],
     infrun:   status->kind = stopped, signal = GDB_SIGNAL_0
     infrun:   Thread 1639.22260 not executing
     infrun:   Thread 1639.22256 not executing
     infrun:   Thread 1639.22258 not executing
     infrun:   Thread 1639.22257 not executing
     infrun:   Thread 1639.22259 not executing
     infrun:   Thread 1639.22255 not executing
     infrun:   Thread 1639.22253 executing, already stopping
     infrun:   Thread 1639.22251 executing, already stopping
     infrun:   Thread 1639.22252 executing, already stopping
     infrun:   Thread 1639.22250 executing, already stopping
     infrun:   Thread 1639.22254 executing, already stopping
     infrun:   Thread 1639.22247 executing, already stopping
     infrun:   Thread 1639.22213 not executing
     infrun:   Thread 1639.22207 not executing
     infrun:   Thread 1639.22201 not executing
     infrun:   Thread 1639.22219 not executing
     infrun:   Thread 1639.1639 not executing
     ** HANG HERE **
    
    GDB is waiting for the stop replies of any of those "already stopping"
    threads.  Take 22253 for example.  On the gdbserver logs we see:
    
     ...
     resume_stop request for LWP 22253
     stopping LWP 22253
     Sending sigstop to lwp 22253
     linux_resume done
     ...
    
    and:
    
     my_waitpid (-1, 0x40000001)
     my_waitpid (-1, 0x80000001): status(3057f), 22253
     LWFE: waitpid(-1, ...) returned 22253, ERRNO-OK
     LLW: waitpid 22253 received Trace/breakpoint trap (stopped)
     pc is 0x3615ef4ce1
     HEW: Got clone event from LWP 22253, new child is LWP 22259
    
    but from here on, we never see any other event for LWP 22253.  In
    particular, we never see the expected SIGSTOP (from "Sending sigstop"
    above).  The issue is that linux_resume_stopped_resumed_lwps never
    re-resumes the 22253 after the clone event.
    
    gdb/gdbserver/ChangeLog:
    2015-11-30  Pedro Alves  <palves@redhat.com>
    
    	* linux-low.c (resume_stopped_resumed_lwps): Don't check whether
    	the thread's last_resume_kind was resume_stop.

Diff:
---
 gdb/gdbserver/ChangeLog   | 5 +++++
 gdb/gdbserver/linux-low.c | 1 -
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 3d694ac..3d00ed4 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,5 +1,10 @@
 2015-11-30  Pedro Alves  <palves@redhat.com>
 
+	* linux-low.c (resume_stopped_resumed_lwps): Don't check whether
+	the thread's last_resume_kind was resume_stop.
+
+2015-11-30  Pedro Alves  <palves@redhat.com>
+
 	* linux-low.c (linux_attach): In non-stop mode, wait for one stop
 	before returning.
 
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 69fda7f..1f7d8d1 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -2409,7 +2409,6 @@ resume_stopped_resumed_lwps (struct inferior_list_entry *entry)
   if (lp->stopped
       && !lp->suspended
       && !lp->status_pending_p
-      && thread->last_resume_kind != resume_stop
       && thread->last_status.kind == TARGET_WAITKIND_IGNORE)
     {
       int step = thread->last_resume_kind == resume_step;