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base: handle twice Lock::lock calls correctly

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to avoid loosing threads in the applicants list if lock owner calls 'twice'
Lock::lock().

Fixes #2300
This commit is contained in:
Alexander Boettcher
2017-03-01 16:21:29 +01:00
committed by Christian Helmuth
parent 8102b78d22
commit 25ac3cdd86
1 changed files with 23 additions and 8 deletions
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31
repos/base/src/lib/base/lock.cc
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@ -23,7 +23,7 @@ using namespace Genode;
static inline Genode::Thread *invalid_thread_base() static inline Genode::Thread *invalid_thread_base()
{ {
return (Genode::Thread*)~0; return (Genode::Thread*)~0UL;
} }
@ -66,10 +66,6 @@ void Cancelable_lock::lock()
spinlock_lock(&_spinlock_state); spinlock_lock(&_spinlock_state);
/* reset ownership if one thread 'lock' twice */
if (_owner == myself)
_owner = Applicant(invalid_thread_base());
if (cmpxchg(&_state, UNLOCKED, LOCKED)) { if (cmpxchg(&_state, UNLOCKED, LOCKED)) {
/* we got the lock */ /* we got the lock */
@ -84,8 +80,28 @@ void Cancelable_lock::lock()
* list of applicants and block for the current lock holder. * list of applicants and block for the current lock holder.
*/ */
_last_applicant->applicant_to_wake_up(&myself); /* reset ownership if one thread 'lock' twice */
_last_applicant = &myself; if (_owner == myself) {
/* remember applicants already in list */
Applicant * applicants =_owner.applicant_to_wake_up();
/* reset owner */
_owner = Applicant(invalid_thread_base());
/* register thread calling twice 'lock' as first applicant */
_owner.applicant_to_wake_up(&myself);
/* if we had already applicants, add after myself in list */
myself.applicant_to_wake_up(applicants);
/* if we had applicants, _last_applicant already points to the last */
if (!applicants)
_last_applicant = &myself;
} else {
_last_applicant->applicant_to_wake_up(&myself);
_last_applicant = &myself;
}
spinlock_unlock(&_spinlock_state); spinlock_unlock(&_spinlock_state);
/* /*
@ -179,4 +195,3 @@ Cancelable_lock::Cancelable_lock(Cancelable_lock::State initial)
if (initial == LOCKED) if (initial == LOCKED)
lock(); lock();
} }