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add comments to the pagefault code

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cl 2003-09-16 15:28:45 +00:00
parent fe74654bab
commit 52a920b5da
1 changed files with 42 additions and 3 deletions
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45
sys/kern/kern_sa.c
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@ -1,4 +1,4 @@
/* $NetBSD: kern_sa.c,v 1.24 2003/09/16 13:46:24 cl Exp $ */
/* $NetBSD: kern_sa.c,v 1.25 2003/09/16 15:28:45 cl Exp $ */
/*-
* Copyright (c) 2001 The NetBSD Foundation, Inc.
@ -37,7 +37,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_sa.c,v 1.24 2003/09/16 13:46:24 cl Exp $");
__KERNEL_RCSID(0, "$NetBSD: kern_sa.c,v 1.25 2003/09/16 15:28:45 cl Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@ -220,6 +220,13 @@ sys_sa_stacks(struct lwp *l, void *v, register_t *retval)
if ((sa->sa_nstacks == 0) && (sa->sa_vp_wait_count != 0))
l->l_flag |= L_SA_UPCALL;
/*
* Save addresses of the first and last stack on initial load
* the pagefault code uses the saved address to detect threads
* running on an upcall stack.
* XXX assumes all stacks are adjoining
* XXX assumes initial load includes all stacks ever used
*/
if (sa->sa_vp_stacks_low == 0) {
sa->sa_vp_stacks_low = (uintptr_t)sa->sa_stacks[0].ss_sp;
sa->sa_vp_stacks_high = (uintptr_t)sa->sa_stacks[count - 1].ss_sp +
@ -428,6 +435,22 @@ sa_preempt(struct lwp *l)
}
/*
* Help userspace library resolve locks and critical sections
* - recycles the calling LWP and its stack if it was not preempted
* and idle the VP until the sa_id LWP unblocks
* - recycles the to be unblocked LWP if the calling LWP was preempted
* and returns control to the userspace library so it can switch to
* the blocked thread
* This is used if a thread blocks because of a pagefault and is in a
* critical section in the userspace library and the critical section
* resolving code cannot continue until the blocked thread is unblocked.
* If the userspace library switches to the blocked thread in the second
* case, it will either continue (because the pagefault has been handled)
* or it will pagefault again. The second pagefault will be detected by
* the double pagefault code and the VP will idle until the pagefault
* has been handled.
*/
int
sys_sa_unblockyield(struct lwp *l, void *v, register_t *retval)
{
@ -653,6 +676,13 @@ sa_upcall_getstate(struct sadata_upcall *sau, struct lwp *event,
}
/*
* Detect double pagefaults and pagefaults on upcalls.
* - double pagefaults are detected by comparing the previous faultaddr
* against the current faultaddr
* - pagefaults on upcalls are detected by checking if the userspace
* thread is running on an upcall stack
*/
static int
sa_pagefault(struct lwp *l, ucontext_t *l_ctx)
{
@ -781,7 +811,16 @@ sa_switch(struct lwp *l, int type)
goto sa_upcall_failed;
}
if (l->l_flag & L_SA_PAGEFAULT && sa_pagefault(l,
/*
* Perform the double/upcall pagefault check.
* We do this only here since we need l's ucontext to
* get l's userspace stack. sa_upcall0 above has saved
* it for us.
* The L_SA_PAGEFAULT flag is set in the MD
* pagefault code to indicate a pagefault. The MD
* pagefault code also saves the faultaddr for us.
*/
if ((l->l_flag & L_SA_PAGEFAULT) && sa_pagefault(l,
&sau->sau_state.captured.e_ctx) != 0) {
sadata_upcall_free(sau);
sa->sa_stacks[sa->sa_nstacks++] = st;