[Bug translator/16614] New: signal forwarding to child processes uses invalid pthread* functions

[Bug translator/16614] New: signal forwarding to child processes uses invalid pthread* functions

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16614

            Bug ID: 16614
           Summary: signal forwarding to child processes uses invalid
                    pthread* functions
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
          Assignee: systemtap at sourceware dot org
          Reporter: fche at redhat dot com

Tracing through stap / stap-serverd signal handling, thence kill_stap_spawn(),
thence spawned_pids_t::killall, one finds pthread mutex lock operations
wrapping
our reading of a set<pid_t>.

That's not appropriate.  We can't call pthread mutex ops from a signal handler
at all; among other reasons, it's a deadlock recipe if the signal comes in at
the wrong time.  We can't just traverse the set<> locklessly either, because it
may be in the middle of being updated by another thread.

We need a signal-safe structure for collecting & iterating child pids.

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[Bug translator/16614] signal forwarding to child processes uses invalid pthread* functions

[jistone at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16614

Josh Stone <jistone at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |jistone at redhat dot com

--- Comment #1 from Josh Stone <jistone at redhat dot com> ---
(In reply to Frank Ch. Eigler from comment #0)
> We need a signal-safe structure for collecting & iterating child pids.

We may just need to make spawned_pids_t properly either-or, signal-safe or
thread-safe but not both.  At the moment, stap is single-threaded and calls
kill_stap_spawn from a signal handler; stap-serverd is multithreaded but only
kills via main.  So stap only needs the signal-masking, and stap-serverd only
needs the pthread mutex.  (In fact, the use of sigprocmask is unspecified in
multithreaded processes.)

This is half-way selected by the SINGLE_THREADED macro now, but that's a big
hammer, not even set by stap.

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