tree 14e10624e9e83a4be2c300087a022fa12c20e11b
parent 16a447bec542b9217710d5e37f14b15a82b5273d
author Thiago Jung Bauermann <thiago.bauermann@linaro.org> 1710654005 -0300
committer Thiago Jung Bauermann <thiago.bauermann@linaro.org> 1714443251 -0300

gdb/nat/linux: Fix attaching to process when it has zombie threads

When GDB attaches to a multi-threaded process, it calls
linux_proc_attach_tgid_threads () to go through all threads found in
/proc/PID/task/ and call attach_proc_task_lwp_callback () on each of
them.  If it does that twice without the callback reporting that a new
thread was found, then it considers that all inferior threads have been
found and returns.

The problem is that the callback considers any thread that it hasn't
attached to yet as new.  This causes problems if the process has one or
more zombie threads, because GDB can't attach to it and the loop will
always "find" a new thread (the zombie one), and get stuck in an
infinite loop.

This is easy to trigger (at least on aarch64-linux and powerpc64le-linux)
with the gdb.threads/attach-many-short-lived-threads.exp testcase, because
its test program constantly creates and finishes joinable threads so the
chance of having zombie threads is high.

This problem causes the following failures:

FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: attach (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: no new threads (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: set breakpoint always-inserted on (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: break break_fn (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: break at break_fn: 1 (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: break at break_fn: 2 (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: break at break_fn: 3 (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: reset timer in the inferior (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: print seconds_left (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: detach (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: set breakpoint always-inserted off (timeout)
FAIL: gdb.threads/attach-many-short-lived-threads.exp: iter 8: delete all breakpoints, watchpoints, tracepoints, and catchpoints in delete_breakpoints (timeout)
ERROR: breakpoints not deleted

The iteration number is random, and all tests in the subsequent iterations
fail too, because GDB is stuck in the attach command at the beginning of
the iteration.

The solution is to make linux_proc_attach_tgid_threads () remember when it
has already processed a given LWP and skip it in the subsequent iterations.

PR testsuite/31312
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31312

Reviewed-By: Luis Machado <luis.machado@arm.com>
Approved-By: Pedro Alves <pedro@palves.net>