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base: entrypoint 'wait_and_dispatch_one_signal'

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There existed a race when 'wait_and_dispatch_one_signal' is called form
a RPC context, because the 'signal_proxy' or 'main' will block and the
signal semaphore, when the EP then calls 'wait_and_dispatch_one_signal',
the signal proxy is woken up ands sends an RPC to the EP, leading to a
dead lock if no further signal arrive, because the EP will then remain
blocked in the signal semaphore.

Therefore, for this case, the signal proxy will now perform a semaphore
up operation and does not perform an RPC if the EP is within
'wait_and_dispatch_one_signal'.
This commit is contained in:
Sebastian Sumpf
2017-02-14 17:00:53 +01:00
committed by Norman Feske
parent 652f92c9c9
commit b66716d278
6 changed files with 79 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files

64
repos/base/src/lib/base/entrypoint.cc
View File

@ -16,6 +16,8 @@
#include <base/entrypoint.h>
#include <base/component.h>
#include <cpu/atomic.h>
#define INCLUDED_BY_ENTRYPOINT_CC /* prevent "deprecated" warning */
#include <cap_session/connection.h>
#undef INCLUDED_BY_ENTRYPOINT_CC
@ -63,17 +65,28 @@ void Entrypoint::_process_incoming_signals()
do {
_sig_rec->block_for_signal();
/*
* It might happen that we try to forward a signal to the
* entrypoint, while the context of that signal is already
* destroyed. In that case we will get an ipc error exception
* as result, which has to be caught.
*/
retry<Genode::Blocking_canceled>(
[&] () { _signal_proxy_cap.call<Signal_proxy::Rpc_signal>(); },
[] () { warning("blocking canceled during signal processing"); }
);
int success = cmpxchg(&_signal_recipient, NONE, SIGNAL_PROXY);
/* common case, entrypoint is not in 'wait_and_dispatch_one_signal' */
if (success) {
/*
* It might happen that we try to forward a signal to the
* entrypoint, while the context of that signal is already
* destroyed. In that case we will get an ipc error exception
* as result, which has to be caught.
*/
retry<Blocking_canceled>(
[&] () { _signal_proxy_cap.call<Signal_proxy::Rpc_signal>(); },
[] () { warning("blocking canceled during signal processing"); });
cmpxchg(&_signal_recipient, SIGNAL_PROXY, NONE);
} else {
/*
* Entrypoint is in 'wait_and_dispatch_one_signal', wakup it up and
* block for next signal
*/
_sig_rec->unblock_signal_waiter(*_rpc_ep);
}
} while (!_suspended);
_suspend_dispatcher.destruct();
@ -107,6 +120,33 @@ void Entrypoint::_process_incoming_signals()
}
void Entrypoint::wait_and_dispatch_one_signal()
{
for (;;) {
try {
{
cmpxchg(&_signal_recipient, NONE, ENTRYPOINT);
Signal sig =_sig_rec->pending_signal();
cmpxchg(&_signal_recipient, ENTRYPOINT, NONE);
_dispatch_signal(sig);
}
_execute_post_signal_hook();
return;
} catch (Signal_receiver::Signal_not_pending) {
_sig_rec->block_for_signal();
}
}
}
void Entrypoint::schedule_suspend(void (*suspended)(), void (*resumed)())
{
_suspended_callback = suspended;
@ -119,7 +159,7 @@ void Entrypoint::schedule_suspend(void (*suspended)(), void (*resumed)())
_suspend_dispatcher.construct(*this, *this, &Entrypoint::_handle_suspend);
/* trigger wakeup of the signal-dispatch loop for suspend */
Genode::Signal_transmitter(*_suspend_dispatcher).submit();
Signal_transmitter(*_suspend_dispatcher).submit();
}
@ -186,7 +226,7 @@ Entrypoint::Entrypoint(Env &env)
try {
constructor_cap.call<Constructor::Rpc_construct>();
} catch (Genode::Blocking_canceled) {
} catch (Blocking_canceled) {
warning("blocking canceled in entrypoint constructor");
}

6
repos/base/src/lib/base/signal.cc
View File

@ -255,6 +255,12 @@ void Signal_receiver::block_for_signal()
}
void Signal_receiver::unblock_signal_waiter(Rpc_entrypoint &)
{
_signal_available.up();
}
void Signal_receiver::local_submit(Signal::Data ns)
{
Signal_context *context = ns.context;