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x86: Restore the critical section around whole ipi_bitmap_handler() if

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hardclock IPI is delivered.

In the current code after r355311, critical section is taken only
around hardclockintr() call, and sched_preempt() is called after the
section is exited. If we reschedule after exit, as we typically would
due to conditions that caused IPI, in ULE the runq tdq_ipipending is
not cleared, which blocks generation of further preempt IPIs.

Since all relatively modern (10 years) hardware has per-cpu event
timers, restoring the critical section conditionally does not affect
it.

Reported and tested by: cy
Diagnosed and reviewed by: jeff (previous version)
Sponsored by:	The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D22716
This commit is contained in:
Konstantin Belousov 2019-12-07 00:28:08 +00:00
parent 3e5b13991c
commit ff326a1879
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=355475
1 changed files with 21 additions and 11 deletions
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32
sys/x86/x86/mp_x86.c
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@ -1262,10 +1262,28 @@ ipi_bitmap_handler(struct trapframe frame)
u_int ipi_bitmap;
td = curthread;
ipi_bitmap = atomic_readandclear_int(&cpuid_to_pcpu[cpu]->
pc_ipi_bitmap);
/*
* sched_preempt() must be called to clear the pending preempt
* IPI to enable delivery of further preempts. However, the
* critical section will cause extra scheduler lock thrashing
* when used unconditionally. Only critical_enter() if
* hardclock must also run, which requires the section entry.
*/
if (ipi_bitmap & (1 << IPI_HARDCLOCK))
critical_enter();
td->td_intr_nesting_level++;
oldframe = td->td_intr_frame;
td->td_intr_frame = &frame;
ipi_bitmap = atomic_readandclear_int(&cpuid_to_pcpu[cpu]->pc_ipi_bitmap);
if (ipi_bitmap & (1 << IPI_PREEMPT)) {
#ifdef COUNT_IPIS
(*ipi_preempt_counts[cpu])++;
#endif
sched_preempt(td);
}
if (ipi_bitmap & (1 << IPI_AST)) {
#ifdef COUNT_IPIS
(*ipi_ast_counts[cpu])++;
@ -1273,23 +1291,15 @@ ipi_bitmap_handler(struct trapframe frame)
/* Nothing to do for AST */
}
if (ipi_bitmap & (1 << IPI_HARDCLOCK)) {
critical_enter();
#ifdef COUNT_IPIS
(*ipi_hardclock_counts[cpu])++;
#endif
hardclockintr();
critical_exit();
}
/* Run preempt after clock handlers since it may switch. */
if (ipi_bitmap & (1 << IPI_PREEMPT)) {
#ifdef COUNT_IPIS
(*ipi_preempt_counts[cpu])++;
#endif
sched_preempt(td);
}
td->td_intr_frame = oldframe;
td->td_intr_nesting_level--;
if (ipi_bitmap & (1 << IPI_HARDCLOCK))
critical_exit();
}
/*