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Code Issues Releases Activity

We can't grab the sched_lock in set_user_ldt() because when it is called

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from cpu_switch(), curproc has been changed, but the sched_lock owner will
not be updated until we return to mi_switch(), thus we deadlock against
ourselves.  As a workaround, push the acquire and release of sched_lock out
to the callers of set_user_ldt().  Note that we can't use a mtx_assert() in
set_user_ldt for the same reason.

Sleuting by:	tmm
Tested by:	tmm, dougb
This commit is contained in:
John Baldwin 2001-05-30 14:35:22 +00:00
parent 79ec1c507a
commit 1acf256d96
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=77486
4 changed files with 50 additions and 12 deletions
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27
sys/amd64/amd64/sys_machdep.c
View File

@ -240,16 +240,16 @@ i386_get_ioperm(p, args)
/*
* Update the GDT entry pointing to the LDT to point to the LDT of the
* current process.
*
* This must be called with sched_lock held. Unfortunately, we can't use a
* mtx_assert() here because cpu_switch() calls this function after changing
* curproc but before sched_lock's owner is updated in mi_switch().
*/
void
set_user_ldt(struct pcb *pcb)
{
struct pcb_ldt *pcb_ldt;
if (pcb != PCPU_GET(curpcb))
return;
mtx_lock_spin(&sched_lock);
pcb_ldt = pcb->pcb_ldt;
#ifdef SMP
gdt[PCPU_GET(cpuid) * NGDT + GUSERLDT_SEL].sd = pcb_ldt->ldt_sd;
@ -258,6 +258,17 @@ set_user_ldt(struct pcb *pcb)
#endif
lldt(GSEL(GUSERLDT_SEL, SEL_KPL));
PCPU_SET(currentldt, GSEL(GUSERLDT_SEL, SEL_KPL));
}
void
set_user_ldt_rv(struct pcb *pcb)
{
if (pcb != PCPU_GET(curpcb))
return;
mtx_lock_spin(&sched_lock);
set_user_ldt(pcb);
mtx_unlock_spin(&sched_lock);
}
@ -422,15 +433,21 @@ i386_set_ldt(p, args)
kmem_free(kernel_map, (vm_offset_t)old_ldt_base,
old_ldt_len * sizeof(union descriptor));
FREE(new_ldt, M_SUBPROC);
#ifndef SMP
mtx_lock_spin(&sched_lock);
#endif
} else {
pcb->pcb_ldt = pcb_ldt = new_ldt;
#ifdef SMP
mtx_unlock_spin(&sched_lock);
#endif
}
#ifdef SMP
/* signal other cpus to reload ldt */
smp_rendezvous(NULL, (void (*)(void *))set_user_ldt, NULL, pcb);
smp_rendezvous(NULL, (void (*)(void *))set_user_ldt_rv, NULL, pcb);
#else
set_user_ldt(pcb);
mtx_unlock_spin(&sched_lock);
#endif
}

4
sys/amd64/amd64/vm_machdep.c
View File

@ -132,9 +132,11 @@ cpu_fork(p1, p2, flags)
struct pcb_ldt *pcb_ldt = pcb1->pcb_ldt;
if (pcb_ldt && pcb_ldt->ldt_refcnt > 1) {
pcb_ldt = user_ldt_alloc(pcb1,pcb_ldt->ldt_len);
user_ldt_free(pcb1);
if (pcb_ldt == NULL)
panic("could not copy LDT");
pcb1->pcb_ldt = pcb_ldt;
set_user_ldt(pcb1);
user_ldt_free(pcb1);
}
}
return;

27
sys/i386/i386/sys_machdep.c
View File

@ -240,16 +240,16 @@ i386_get_ioperm(p, args)
/*
* Update the GDT entry pointing to the LDT to point to the LDT of the
* current process.
*
* This must be called with sched_lock held. Unfortunately, we can't use a
* mtx_assert() here because cpu_switch() calls this function after changing
* curproc but before sched_lock's owner is updated in mi_switch().
*/
void
set_user_ldt(struct pcb *pcb)
{
struct pcb_ldt *pcb_ldt;
if (pcb != PCPU_GET(curpcb))
return;
mtx_lock_spin(&sched_lock);
pcb_ldt = pcb->pcb_ldt;
#ifdef SMP
gdt[PCPU_GET(cpuid) * NGDT + GUSERLDT_SEL].sd = pcb_ldt->ldt_sd;
@ -258,6 +258,17 @@ set_user_ldt(struct pcb *pcb)
#endif
lldt(GSEL(GUSERLDT_SEL, SEL_KPL));
PCPU_SET(currentldt, GSEL(GUSERLDT_SEL, SEL_KPL));
}
void
set_user_ldt_rv(struct pcb *pcb)
{
if (pcb != PCPU_GET(curpcb))
return;
mtx_lock_spin(&sched_lock);
set_user_ldt(pcb);
mtx_unlock_spin(&sched_lock);
}
@ -422,15 +433,21 @@ i386_set_ldt(p, args)
kmem_free(kernel_map, (vm_offset_t)old_ldt_base,
old_ldt_len * sizeof(union descriptor));
FREE(new_ldt, M_SUBPROC);
#ifndef SMP
mtx_lock_spin(&sched_lock);
#endif
} else {
pcb->pcb_ldt = pcb_ldt = new_ldt;
#ifdef SMP
mtx_unlock_spin(&sched_lock);
#endif
}
#ifdef SMP
/* signal other cpus to reload ldt */
smp_rendezvous(NULL, (void (*)(void *))set_user_ldt, NULL, pcb);
smp_rendezvous(NULL, (void (*)(void *))set_user_ldt_rv, NULL, pcb);
#else
set_user_ldt(pcb);
mtx_unlock_spin(&sched_lock);
#endif
}

4
sys/i386/i386/vm_machdep.c
View File

@ -132,9 +132,11 @@ cpu_fork(p1, p2, flags)
struct pcb_ldt *pcb_ldt = pcb1->pcb_ldt;
if (pcb_ldt && pcb_ldt->ldt_refcnt > 1) {
pcb_ldt = user_ldt_alloc(pcb1,pcb_ldt->ldt_len);
user_ldt_free(pcb1);
if (pcb_ldt == NULL)
panic("could not copy LDT");
pcb1->pcb_ldt = pcb_ldt;
set_user_ldt(pcb1);
user_ldt_free(pcb1);
}
}
return;