Commit dbba4b55 authored by Peter Chubb's avatar Peter Chubb Committed by David Mosberger

[PATCH] ia64: Fix OSDL BugMe report 2885: realtime process can't preempt low...

[PATCH] ia64: Fix OSDL BugMe report 2885: realtime process can't preempt low priority process in kernel

Rearranged code to make it work. There were two problems:

 1. The preempt flag was being tested only if code was leaving for
    user space (the logic should be: test for RESCHEDULE if we're
    switching to a kernel thread, test everything if switching to a
    user thread)

 2. The check of the user space flags was being repeated even if the
    work had been done.

There is one small change in semantics: when returning from a
preemption, the preemption flag will *not* be rechecked.  Otherwise, I
found that it was easy to get into a livelock situation where no
forward progress was made.
Signed-off-by: default avatarDavid Mosberger <davidm@hpl.hp.com>
parent 43159b43
......@@ -663,25 +663,31 @@ GLOBAL_ENTRY(ia64_leave_syscall)
PT_REGS_UNWIND_INFO(0)
/*
* work.need_resched etc. mustn't get changed by this CPU before it returns to
* user- or fsys-mode, hence we disable interrupts early on:
* user- or fsys-mode, hence we disable interrupts early on.
*
* p6 controls whether current_thread_info()->flags needs to be check for
* extra work. We always check for extra work when returning to user-level.
* With CONFIG_PREEMPT, we also check for extra work when the preempt_count
* is 0. After extra work processing has been completed, execution
* resumes at .work_processed_syscall with p6 set to 1 if the extra-work-check
* needs to be redone.
*/
#ifdef CONFIG_PREEMPT
rsm psr.i // disable interrupts
#else
(pUStk) rsm psr.i
#endif
cmp.eq pLvSys,p0=r0,r0 // pLvSys=1: leave from syscall
(pUStk) cmp.eq.unc p6,p0=r0,r0 // p6 <- pUStk
.work_processed_syscall:
#ifdef CONFIG_PREEMPT
(pKStk) adds r20=TI_PRE_COUNT+IA64_TASK_SIZE,r13
;;
.pred.rel.mutex pUStk,pKStk
(pKStk) ld4 r21=[r20] // r21 <- preempt_count
(pUStk) mov r21=0 // r21 <- 0
;;
(p6) cmp.eq.unc p6,p0=r21,r0 // p6 <- p6 && (r21 == 0)
#endif /* CONFIG_PREEMPT */
cmp.eq p6,p0=r21,r0 // p6 <- pUStk || (preempt_count == 0)
#else /* !CONFIG_PREEMPT */
(pUStk) rsm psr.i
cmp.eq pLvSys,p0=r0,r0 // pLvSys=1: leave from syscall
(pUStk) cmp.eq.unc p6,p0=r0,r0 // p6 <- pUStk
#endif
.work_processed_syscall:
adds r16=PT(LOADRS)+16,r12
adds r17=PT(AR_BSPSTORE)+16,r12
adds r18=TI_FLAGS+IA64_TASK_SIZE,r13
......@@ -776,26 +782,31 @@ GLOBAL_ENTRY(ia64_leave_kernel)
PT_REGS_UNWIND_INFO(0)
/*
* work.need_resched etc. mustn't get changed by this CPU before it returns to
* user- or fsys-mode, hence we disable interrupts early on:
* user- or fsys-mode, hence we disable interrupts early on.
*
* p6 controls whether current_thread_info()->flags needs to be check for
* extra work. We always check for extra work when returning to user-level.
* With CONFIG_PREEMPT, we also check for extra work when the preempt_count
* is 0. After extra work processing has been completed, execution
* resumes at .work_processed_syscall with p6 set to 1 if the extra-work-check
* needs to be redone.
*/
#ifdef CONFIG_PREEMPT
rsm psr.i // disable interrupts
#else
(pUStk) rsm psr.i
#endif
cmp.eq p0,pLvSys=r0,r0 // pLvSys=0: leave from kernel
(pUStk) cmp.eq.unc p6,p0=r0,r0 // p6 <- pUStk
;;
.work_processed_kernel:
#ifdef CONFIG_PREEMPT
adds r20=TI_PRE_COUNT+IA64_TASK_SIZE,r13
(pKStk) adds r20=TI_PRE_COUNT+IA64_TASK_SIZE,r13
;;
.pred.rel.mutex pUStk,pKStk
(pKStk) ld4 r21=[r20] // r21 <- preempt_count
(pUStk) mov r21=0 // r21 <- 0
;;
(p6) cmp.eq.unc p6,p0=r21,r0 // p6 <- p6 && (r21 == 0)
#endif /* CONFIG_PREEMPT */
cmp.eq p6,p0=r21,r0 // p6 <- pUStk || (preempt_count == 0)
#else
(pUStk) rsm psr.i
cmp.eq p0,pLvSys=r0,r0 // pLvSys=0: leave from kernel
(pUStk) cmp.eq.unc p6,p0=r0,r0 // p6 <- pUStk
#endif
.work_processed_kernel:
adds r17=TI_FLAGS+IA64_TASK_SIZE,r13
;;
(p6) ld4 r31=[r17] // load current_thread_info()->flags
......@@ -1065,7 +1076,7 @@ skip_rbs_switch:
br.cond.sptk.many .work_processed_kernel // re-check
.notify:
br.call.spnt.many rp=notify_resume_user
(pUStk) br.call.spnt.many rp=notify_resume_user
.ret10: cmp.ne p6,p0=r0,r0 // p6 <- 0
(pLvSys)br.cond.sptk.many .work_processed_syscall // don't re-check
br.cond.sptk.many .work_processed_kernel // don't re-check
......
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