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Kernel: Acquire reference to waitee before trying to block in sys$waitid

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Previously, we would try to acquire a reference to the all processes
lock or other contended resources while holding both the scheduler lock
and the thread's blocker lock. This could lead to a deadlock if we
actually have to block on those other resources.
This commit is contained in:
Andrew Kaster 2021-08-22 22:01:04 -06:00 • committed by Andreas Kling
parent dea62fe93c
commit 54161bf5b4
4 changed files with 43 additions and 66 deletions
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27
Kernel/Syscalls/waitid.cpp
View file

@ -4,15 +4,16 @@
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Variant.h>
#include <Kernel/Debug.h>
#include <Kernel/Process.h>
namespace Kernel {
KResultOr<siginfo_t> Process::do_waitid(idtype_t idtype, int id, int options)
KResultOr<siginfo_t> Process::do_waitid(Variant<Empty, NonnullRefPtr<Process>, NonnullRefPtr<ProcessGroup>> waitee, int options)
{
KResultOr<siginfo_t> result = KResult(KSuccess);
if (Thread::current()->block<Thread::WaitBlocker>({}, options, idtype, id, result).was_interrupted())
if (Thread::current()->block<Thread::WaitBlocker>({}, options, move(waitee), result).was_interrupted())
return EINTR;
VERIFY(!result.is_error() || (options & WNOHANG) || result.error() != KSuccess);
return result;
@ -27,18 +28,34 @@ KResultOr<FlatPtr> Process::sys$waitid(Userspace<const Syscall::SC_waitid_params
if (!copy_from_user(&params, user_params))
return EFAULT;
Variant<Empty, NonnullRefPtr<Process>, NonnullRefPtr<ProcessGroup>> waitee = Empty {};
switch (params.idtype) {
case P_ALL:
case P_PID:
case P_PGID:
waitee = Empty {};
break;
case P_PID: {
auto waitee_process = Process::from_pid(params.id);
if (!waitee_process || waitee_process->ppid() != Process::current().pid()) {
return ECHILD;
}
waitee = waitee_process.release_nonnull();
break;
}
case P_PGID: {
auto waitee_group = ProcessGroup::from_pgid(params.id);
if (!waitee_group) {
return ECHILD;
}
waitee = waitee_group.release_nonnull();
break;
}
default:
return EINVAL;
}
dbgln_if(PROCESS_DEBUG, "sys$waitid({}, {}, {}, {})", params.idtype, params.id, params.infop, params.options);
auto siginfo_or_error = do_waitid(static_cast<idtype_t>(params.idtype), params.id, params.options);
auto siginfo_or_error = do_waitid(move(waitee), params.options);
if (siginfo_or_error.is_error())
return siginfo_or_error.error();