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hw: fix race in signal dispatching

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There was a race when the component entrypoint wanted to do
'wait_and_dispatch_one_signal'. In this function it raises a flag for
the signal proxy thread to notice that the entrypoint also wants to
block for signals. When the flag is set and the signal proxy wakes up
with a new signal, it tried to cancel the blocking of the entrypoint.
However, if the entrypoint had not reached the signal blocking at this
point, the cancel blocking failed without a solution. Now, the new
Kernel::cancel_next_signal_blocking call solves the problem by storing a
request to cancel the next signal blocking of a thread immediately
without blocking itself.

Ref #2284
This commit is contained in:
Martin Stein 2017-02-24 14:29:29 +01:00 committed by Christian Helmuth
parent 2000b7c0e6
commit 56cafb3b57
7 changed files with 123 additions and 49 deletions
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53
repos/base-hw/include/kernel/interface.h
View File

@ -23,24 +23,25 @@ namespace Kernel
/**
* Kernel names of the kernel calls
*/
constexpr Call_arg call_id_stop_thread() { return 0; }
constexpr Call_arg call_id_restart_thread() { return 1; }
constexpr Call_arg call_id_yield_thread() { return 2; }
constexpr Call_arg call_id_send_request_msg() { return 3; }
constexpr Call_arg call_id_send_reply_msg() { return 4; }
constexpr Call_arg call_id_await_request_msg() { return 5; }
constexpr Call_arg call_id_kill_signal_context() { return 6; }
constexpr Call_arg call_id_submit_signal() { return 7; }
constexpr Call_arg call_id_await_signal() { return 8; }
constexpr Call_arg call_id_ack_signal() { return 9; }
constexpr Call_arg call_id_print_char() { return 10; }
constexpr Call_arg call_id_update_data_region() { return 11; }
constexpr Call_arg call_id_update_instr_region() { return 12; }
constexpr Call_arg call_id_ack_cap() { return 13; }
constexpr Call_arg call_id_delete_cap() { return 14; }
constexpr Call_arg call_id_timeout() { return 15; }
constexpr Call_arg call_id_timeout_age_us() { return 16; }
constexpr Call_arg call_id_timeout_max_us() { return 17; }
constexpr Call_arg call_id_stop_thread() { return 0; }
constexpr Call_arg call_id_restart_thread() { return 1; }
constexpr Call_arg call_id_yield_thread() { return 2; }
constexpr Call_arg call_id_send_request_msg() { return 3; }
constexpr Call_arg call_id_send_reply_msg() { return 4; }
constexpr Call_arg call_id_await_request_msg() { return 5; }
constexpr Call_arg call_id_kill_signal_context() { return 6; }
constexpr Call_arg call_id_submit_signal() { return 7; }
constexpr Call_arg call_id_await_signal() { return 8; }
constexpr Call_arg call_id_cancel_next_await_signal() { return 9; }
constexpr Call_arg call_id_ack_signal() { return 10; }
constexpr Call_arg call_id_print_char() { return 11; }
constexpr Call_arg call_id_update_data_region() { return 12; }
constexpr Call_arg call_id_update_instr_region() { return 13; }
constexpr Call_arg call_id_ack_cap() { return 14; }
constexpr Call_arg call_id_delete_cap() { return 15; }
constexpr Call_arg call_id_timeout() { return 16; }
constexpr Call_arg call_id_timeout_age_us() { return 17; }
constexpr Call_arg call_id_timeout_max_us() { return 18; }
/*****************************************************************
@ -281,6 +282,22 @@ namespace Kernel
return call(call_id_await_signal(), receiver_id);
}
/**
* Request to cancel the next signal blocking of a local thread
*
* \param thread_id capability id of the targeted thread
*
* Does not block. Targeted thread must be in the same PD as the caller.
* If the targeted thread is in a signal blocking, cancels the blocking
* directly. Otherwise, stores the request and avoids the next signal
* blocking of the targeted thread as if it was immediately cancelled.
* If the target thread already holds a request, further ones get ignored.
*/
inline void cancel_next_await_signal(capid_t const thread_id)
{
call(call_id_cancel_next_await_signal(), thread_id);
}
/**
* Trigger a specific signal context

2
repos/base-hw/src/core/include/kernel/thread.h
View File

@ -109,6 +109,7 @@ class Kernel::Thread
char const * const _label;
capid_t _timeout_sigid = 0;
bool _paused = false;
bool _cancel_next_await_signal = false;
void _init();
@ -210,6 +211,7 @@ class Kernel::Thread
void _call_update_instr_region();
void _call_print_char();
void _call_await_signal();
void _call_cancel_next_await_signal();
void _call_submit_signal();
void _call_ack_signal();
void _call_kill_signal_context();

68
repos/base-hw/src/core/kernel/thread.cc
View File

@ -404,6 +404,12 @@ void Thread::_call_print_char() { Kernel::log((char)user_arg_1()); }
void Thread::_call_await_signal()
{
/* cancel if another thread set our "cancel next await signal" bit */
if (_cancel_next_await_signal) {
user_arg_0(-1);
_cancel_next_await_signal = false;
return;
}
/* lookup receiver */
Signal_receiver * const r = pd()->cap_tree().find<Signal_receiver>(user_arg_1());
if (!r) {
@ -422,6 +428,31 @@ void Thread::_call_await_signal()
}
void Thread::_call_cancel_next_await_signal()
{
/* kill the caller if he has no protection domain */
if (!pd()) {
error(*this, ": PD not set");
_die();
return;
}
/* kill the caller if the capability of the target thread is invalid */
Thread * const thread = pd()->cap_tree().find<Thread>(user_arg_1());
if (!thread || pd() != thread->pd()) {
error(*this, ": failed to lookup thread ", (unsigned)user_arg_1());
_die();
return;
}
/* resume the target thread directly if it blocks for signals */
if (thread->_state == AWAITS_SIGNAL) {
thread->_cancel_blocking();
return;
}
/* if not, keep in mind to cancel its next signal blocking */
thread->_cancel_next_await_signal = true;
}
void Thread::_call_submit_signal()
{
/* lookup signal context */
@ -545,24 +576,25 @@ void Thread::_call()
/* switch over unrestricted kernel calls */
unsigned const call_id = user_arg_0();
switch (call_id) {
case call_id_update_data_region(): _call_update_data_region(); return;
case call_id_update_instr_region(): _call_update_instr_region(); return;
case call_id_stop_thread(): _call_stop_thread(); return;
case call_id_restart_thread(): _call_restart_thread(); return;
case call_id_yield_thread(): _call_yield_thread(); return;
case call_id_send_request_msg(): _call_send_request_msg(); return;
case call_id_send_reply_msg(): _call_send_reply_msg(); return;
case call_id_await_request_msg(): _call_await_request_msg(); return;
case call_id_kill_signal_context(): _call_kill_signal_context(); return;
case call_id_submit_signal(): _call_submit_signal(); return;
case call_id_await_signal(): _call_await_signal(); return;
case call_id_ack_signal(): _call_ack_signal(); return;
case call_id_print_char(): _call_print_char(); return;
case call_id_ack_cap(): _call_ack_cap(); return;
case call_id_delete_cap(): _call_delete_cap(); return;
case call_id_timeout(): _call_timeout(); return;
case call_id_timeout_age_us(): _call_timeout_age_us(); return;
case call_id_timeout_max_us(): _call_timeout_max_us(); return;
case call_id_update_data_region(): _call_update_data_region(); return;
case call_id_update_instr_region(): _call_update_instr_region(); return;
case call_id_stop_thread(): _call_stop_thread(); return;
case call_id_restart_thread(): _call_restart_thread(); return;
case call_id_yield_thread(): _call_yield_thread(); return;
case call_id_send_request_msg(): _call_send_request_msg(); return;
case call_id_send_reply_msg(): _call_send_reply_msg(); return;
case call_id_await_request_msg(): _call_await_request_msg(); return;
case call_id_kill_signal_context(): _call_kill_signal_context(); return;
case call_id_submit_signal(): _call_submit_signal(); return;
case call_id_await_signal(): _call_await_signal(); return;
case call_id_cancel_next_await_signal(): _call_cancel_next_await_signal(); return;
case call_id_ack_signal(): _call_ack_signal(); return;
case call_id_print_char(): _call_print_char(); return;
case call_id_ack_cap(): _call_ack_cap(); return;
case call_id_delete_cap(): _call_delete_cap(); return;
case call_id_timeout(): _call_timeout(); return;
case call_id_timeout_age_us(): _call_timeout_age_us(); return;
case call_id_timeout_max_us(): _call_timeout_max_us(); return;
default:
/* check wether this is a core thread */
if (!_core()) {

5
repos/base-hw/src/lib/base/signal.cc
View File

@ -19,6 +19,8 @@
#include <base/trace/events.h>
/* base-internal includes */
#include <base/internal/native_thread.h>
#include <base/internal/lock_helper.h>
#include <base/internal/native_utcb.h>
#include <base/internal/native_env.h>
#include <base/internal/capability_space.h>
@ -135,8 +137,7 @@ void Signal_receiver::block_for_signal()
void Signal_receiver::unblock_signal_waiter(Rpc_entrypoint &rpc_ep)
{
/* force ep out of 'await_signal' in 'block_for_signal' */
rpc_ep.cancel_blocking();
Kernel::cancel_next_await_signal(native_thread_id(&rpc_ep));
}

2
repos/base/include/base/entrypoint.h
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@ -94,6 +94,8 @@ class Genode::Entrypoint : Genode::Noncopyable
};
int _signal_recipient { NONE };
Genode::Lock _signal_pending_lock;
Genode::Lock _signal_pending_ack_lock;
Post_signal_hook *_post_signal_hook = nullptr;
void _execute_post_signal_hook()

10
repos/base/include/base/rpc_server.h
View File

@ -31,6 +31,8 @@ namespace Genode {
class Rpc_object_base;
template <typename, typename> struct Rpc_object;
class Rpc_entrypoint;
class Signal_receiver;
}
@ -293,6 +295,14 @@ struct Genode::Rpc_object : Rpc_object_base, Rpc_dispatcher<RPC_INTERFACE, SERVE
*/
class Genode::Rpc_entrypoint : Thread, public Object_pool<Rpc_object_base>
{
/**
* This is only needed because in 'base-hw' we need the Thread
* pointer of the entrypoint to cancel its next signal blocking.
* Remove it as soon as signal dispatching in 'base-hw' doesn't need
* multiple threads anymore.
*/
friend class Signal_receiver;
private:
/**

32
repos/base/src/lib/base/entrypoint.cc
View File

@ -65,7 +65,11 @@ void Entrypoint::_process_incoming_signals()
do {
_sig_rec->block_for_signal();
int success = cmpxchg(&_signal_recipient, NONE, SIGNAL_PROXY);
int success;
{
Lock::Guard guard(_signal_pending_lock);
success = cmpxchg(&_signal_recipient, NONE, SIGNAL_PROXY);
}
/* common case, entrypoint is not in 'wait_and_dispatch_one_signal' */
if (success) {
@ -86,6 +90,11 @@ void Entrypoint::_process_incoming_signals()
* block for next signal
*/
_sig_rec->unblock_signal_waiter(*_rpc_ep);
/*
* wait for the acknowledgment by the entrypoint
*/
_signal_pending_ack_lock.lock();
}
} while (!_suspended);
@ -125,25 +134,26 @@ void Entrypoint::wait_and_dispatch_one_signal()
for (;;) {
try {
_signal_pending_lock.lock();
{
cmpxchg(&_signal_recipient, NONE, ENTRYPOINT);
cmpxchg(&_signal_recipient, NONE, ENTRYPOINT);
Signal sig =_sig_rec->pending_signal();
cmpxchg(&_signal_recipient, ENTRYPOINT, NONE);
Signal sig =_sig_rec->pending_signal();
_signal_pending_lock.unlock();
cmpxchg(&_signal_recipient, ENTRYPOINT, NONE);
_signal_pending_ack_lock.unlock();
_dispatch_signal(sig);
}
_execute_post_signal_hook();
return;
_dispatch_signal(sig);
break;
} catch (Signal_receiver::Signal_not_pending) {
_signal_pending_lock.unlock();
_sig_rec->block_for_signal();
}
}
_execute_post_signal_hook();
}