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From: "ctice42 at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug server/13279] New: gdbserver hangs (multi-threaded) if stepping
 on one thread & another thread gets SIGPROF
Date: Mon, 10 Oct 2011 23:30:00 -0000
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http://sourceware.org/bugzilla/show_bug.cgi?id=13279

             Bug #: 13279
           Summary: gdbserver hangs (multi-threaded) if stepping on one
                    thread & another thread gets SIGPROF
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: server
        AssignedTo: unassigned@sourceware.org
        ReportedBy: ctice42@gmail.com
    Classification: Unclassified


Created attachment 5973
  --> http://sourceware.org/bugzilla/attachment.cgi?id=5973
test program to generate multiple threads that get lots of SIGPROFs.

Running gdbserver on a multi-threaded process, whose threads receive lots of
SIGPROF signals, gdbserver hangs while single-stepping if a SIGPROF comes in
during the single-step.  This is on Linux, using current ToT gdb.

To reproduce this:

1. compile the attached test program:

   gcc -g -lpthread -lm -Wall thread-signal-test.c

2. start gdbserver on the result:

   gdbserver :1234 a.out

3. start gdb & connect to gdbserver:

   gdb
   (gdb) file a.out
   (gdb) target remote :1234

4. Set a breakpoint in 'foo' and continue:

    (gdb) b foo
    (gdb) c

5. Do a 'next':

    (gdb) n

6.  Hold down the 'enter' key to get many repeated 'nexts' quickly.

Result:  gdbserver will hang within 10-20 'next's (sometimes a few more,
sometimes a few less).

>>From examining the gdbserver code, it appears that all the threads get stopped
in order to do the single-step; while preparing to do the single-step a SIGPROF
comes in on one of the other threads, in handling the SIGPROF, gdb forgets it
was in the middle of the single-step, and the single-step never gets finished
and the threads never get resumed.

I'm not very familiar with this code so I would appreciate it if someone who is
would take a look at this.

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