kqueue: drain kqueue taskqueue if syscall tickled it
Otherwise return from the syscall and next syscall, which could be kevent(2) on the kqueue that should be notified, races with the kqueue taskqueue thread, and potentially misses the wakeup. This is reliably visible when kevent(2) only peeks into events using zeroed timeout. PR: 258310 Reported by: arichardson, Jan Kokemüller <jan.kokemueller@gmail.com> Reviewed by: arichardson, markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D31858
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@ -1768,9 +1768,16 @@ kqueue_release(struct kqueue *kq, int locked)
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KQ_UNLOCK(kq);
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}
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void
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kqueue_drain_schedtask(void)
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{
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taskqueue_quiesce(taskqueue_kqueue_ctx);
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}
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static void
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kqueue_schedtask(struct kqueue *kq)
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{
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struct thread *td;
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KQ_OWNED(kq);
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KASSERT(((kq->kq_state & KQ_TASKDRAIN) != KQ_TASKDRAIN),
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@ -1779,6 +1786,10 @@ kqueue_schedtask(struct kqueue *kq)
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if ((kq->kq_state & KQ_TASKSCHED) != KQ_TASKSCHED) {
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taskqueue_enqueue(taskqueue_kqueue_ctx, &kq->kq_task);
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kq->kq_state |= KQ_TASKSCHED;
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td = curthread;
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thread_lock(td);
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td->td_flags |= TDF_ASTPENDING | TDF_KQTICKLED;
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thread_unlock(td);
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}
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}
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@ -53,6 +53,7 @@ __FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/bus.h>
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#include <sys/capsicum.h>
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#include <sys/event.h>
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#include <sys/kernel.h>
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#include <sys/lock.h>
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#include <sys/msan.h>
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@ -241,7 +242,8 @@ ast(struct trapframe *framep)
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thread_lock(td);
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flags = td->td_flags;
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td->td_flags &= ~(TDF_ASTPENDING | TDF_NEEDSIGCHK | TDF_NEEDSUSPCHK |
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TDF_NEEDRESCHED | TDF_ALRMPEND | TDF_PROFPEND | TDF_MACPEND);
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TDF_NEEDRESCHED | TDF_ALRMPEND | TDF_PROFPEND | TDF_MACPEND |
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TDF_KQTICKLED);
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thread_unlock(td);
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VM_CNT_INC(v_trap);
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@ -343,6 +345,9 @@ ast(struct trapframe *framep)
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resched_sigs = false;
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}
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if ((flags & TDF_KQTICKLED) != 0)
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kqueue_drain_schedtask();
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/*
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* Handle deferred update of the fast sigblock value, after
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* the postsig() loop was performed.
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@ -349,6 +349,7 @@ int kqfd_register(int fd, struct kevent *kev, struct thread *p,
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int mflag);
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int kqueue_add_filteropts(int filt, struct filterops *filtops);
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int kqueue_del_filteropts(int filt);
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void kqueue_drain_schedtask(void);
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#else /* !_KERNEL */
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@ -451,7 +451,7 @@ do { \
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#define TDF_ALLPROCSUSP 0x00000200 /* suspended by SINGLE_ALLPROC */
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#define TDF_BOUNDARY 0x00000400 /* Thread suspended at user boundary */
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#define TDF_ASTPENDING 0x00000800 /* Thread has some asynchronous events. */
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#define TDF_UNUSED12 0x00001000 /* --available-- */
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#define TDF_KQTICKLED 0x00001000 /* AST drain kqueue taskqueue */
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#define TDF_SBDRY 0x00002000 /* Stop only on usermode boundary. */
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#define TDF_UPIBLOCKED 0x00004000 /* Thread blocked on user PI mutex. */
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#define TDF_NEEDSUSPCHK 0x00008000 /* Thread may need to suspend. */
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