[Bug threads/31512] New: gdb.threads/attach-many-short-lived-threads.exp sometimes fails with "process 2689792 is already traced by process 2039527"

["thiago.bauermann at linaro dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31512

            Bug ID: 31512
           Summary: gdb.threads/attach-many-short-lived-threads.exp
                    sometimes fails with "process 2689792 is already
                    traced by process 2039527"
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: threads
          Assignee: unassigned at sourceware dot org
          Reporter: thiago.bauermann at linaro dot org
  Target Milestone: ---

When running gdb.threads/attach-many-short-lived-threads.exp in a loop, very
rarely an attach command can fail with:

   (gdb) attach 2039552
   Attaching to process 2039552
   Cannot attach to lwp 2689792: Operation not permitted (1), process 2689792
is already traced by process 2039527

PID 2039552 is the testcase inferior, and 2039527 is GDB. GDB didn't report any
success in attaching to the process so the message is surprising.

I was also able to reproduce by doing manually what the testcase does: running
the attach-many-short-lived-threads test program in one terminal and then
repeatedly trying to attach to it from GDB in another terminal

This is hard to reproduce though. In thousands of testcase runs, I saw it only
twice.

Probably not relevant, but I saw this on aarch64-linux running Ubuntu 22.04.3
LTS and kernel 5.4.0-131-generic.

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