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Kernel: Unblock SignalBlocker if a signal was just unmarked as pending

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When updating the signal mask, there is a small frame where we might set
up the receiving process for handing the signal and therefore remove
that signal from the list of pending signals before SignalBlocker has a
chance to block. In turn, this might cause SignalBlocker to never notice
that the signal arrives and it will never unblock once blocked.

Track the currently handled signal separately and include it when
determining if SignalBlocker should be unblocking.
This commit is contained in:
Tim Schumacher 2022-06-30 13:36:03 +02:00 committed by Brian Gianforcaro
parent cd189999d1
commit edbffb3c7a
Notes: sideshowbarker 2024-07-17 09:35:25 +09:00 
Author: https://github.com/timschumi
Commit: https://github.com/SerenityOS/serenity/commit/edbffb3c7a
Pull-request: https://github.com/SerenityOS/serenity/pull/13971
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/Hendiadyoin1
Reviewed-by: https://github.com/bgianfo ✅
Reviewed-by: https://github.com/kleinesfilmroellchen
Reviewed-by: https://github.com/linusg
4 changed files with 13 additions and 1 deletions
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1
Kernel/Syscalls/sigaction.cpp
View file

@ -104,6 +104,7 @@ ErrorOr<FlatPtr> Process::sys$sigreturn([[maybe_unused]] RegisterState& register
auto saved_ax = TRY(copy_typed_from_user<FlatPtr>(stack_ptr));
Thread::current()->m_signal_mask = ucontext.uc_sigmask;
Thread::current()->m_currently_handled_signal = 0;
#if ARCH(X86_64)
auto sp = registers.rsp;
#elif ARCH(I386)

2
Kernel/Thread.cpp
View file

@ -1052,6 +1052,8 @@ DispatchSignalResult Thread::dispatch_signal(u8 signal)
ScopedAddressSpaceSwitcher switcher(m_process);
m_currently_handled_signal = signal;
u32 old_signal_mask = m_signal_mask;
u32 new_signal_mask = m_signal_action_masks[signal].value_or(action.mask);
if ((action.flags & SA_NODEFER) == SA_NODEFER)

1
Kernel/Thread.h
View file

@ -1210,6 +1210,7 @@ private:
u32 m_ticks_in_user { 0 };
u32 m_ticks_in_kernel { 0 };
u32 m_pending_signals { 0 };
u8 m_currently_handled_signal { 0 };
u32 m_signal_mask { 0 };
FlatPtr m_alternative_signal_stack { 0 };
FlatPtr m_alternative_signal_stack_size { 0 };

10
Kernel/ThreadBlockers.cpp
View file

@ -474,7 +474,15 @@ bool Thread::SignalBlocker::check_pending_signals(bool from_add_blocker)
if (m_did_unblock)
return false;
auto matching_pending_signal = bit_scan_forward(thread().pending_signals() & m_pending_set);
auto pending_signals = thread().pending_signals() & m_pending_set;
// Also unblock if we have just "handled" that signal and are in the procecss
// of running their signal handler (i.e. we just unmarked the signal as pending).
if (thread().m_currently_handled_signal)
pending_signals |= (1 << (thread().m_currently_handled_signal - 1)) & m_pending_set;
auto matching_pending_signal = bit_scan_forward(pending_signals);
if (matching_pending_signal == 0)
return false;