From 3f902886a81c6d4e6c399760936b645b5c7a7342 Mon Sep 17 00:00:00 2001 From: Grant Grundler Date: Thu, 17 Nov 2005 16:26:20 -0500 Subject: [PATCH] [PARISC] Disable nesting of interrupts Disable nesting of interrupts - still has holes The offending sequence starts out like this: 1) take external interrupt 2) set_eiem() to only allow TIMER_IRQ; local interrupts still disabled 3) read the EIRR to get a "list" of pending interrupts 4) clear EIRR of pending interrupts we intend to handle 5) call __do_IRQ() to handle IRQ. 6) handle_IRQ_event() enables local interrupts (I-Bit) 7) take a timer interrupt 8) read EIRR to get a new list of pending interrupts 9) clear EIRR of pending interrupts we just read 10) handle pending interrupts found in (8) 11) set_eiem(cpu_eiem) and return [ TROUBLE! all enabled CPU IRQs are unmasked. } 12) handle remaining interrupts pending from (3) e.g. call __do_IRQ() -> handle_IRQ_event()..etc [ TROUBLE! call to handle_IRQ_event() can now enable *any* IRQ. } 13) set_eiem(cpu_eiem) and return The problem is we now get into ugly race conditions with Timer and IPI interrupts at this point. I'm not exactly sure what happens when things go wrong (perhaps nest calls to IPI or timer interrupt?). But I'm certain it's not good. This sequence will break sooner if (10) would accidentally leave interrupts enabled. I'm pretty sure the right answer is now to make cpu_eiem a per CPU variable since all external interrupts on parisc are per CPU. This means we will NOT need to send an IPI to every CPU in the system when enabling or disabling an IRQ since only one CPU needs to change it's EIEM. Thanks to James Bottomley for (once again) pointing out the problem. Signed-off-by: Grant Grundler Signed-off-by: Kyle McMartin --- arch/parisc/kernel/irq.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/arch/parisc/kernel/irq.c b/arch/parisc/kernel/irq.c index f7ae2bcd49a5..21a9c5ad580b 100644 --- a/arch/parisc/kernel/irq.c +++ b/arch/parisc/kernel/irq.c @@ -250,10 +250,11 @@ void do_cpu_irq_mask(struct pt_regs *regs) irq_enter(); /* - * Only allow interrupt processing to be interrupted by the - * timer tick + * Don't allow TIMER or IPI nested interrupts. + * Allowing any single interrupt to nest can lead to that CPU + * handling interrupts with all enabled interrupts unmasked. */ - set_eiem(EIEM_MASK(TIMER_IRQ)); + set_eiem(0UL); /* 1) only process IRQs that are enabled/unmasked (cpu_eiem) * 2) We loop here on EIRR contents in order to avoid @@ -267,9 +268,6 @@ void do_cpu_irq_mask(struct pt_regs *regs) if (!eirr_val) break; - if (eirr_val & EIEM_MASK(TIMER_IRQ)) - set_eiem(0); - mtctl(eirr_val, 23); /* reset bits we are going to process */ /* Work our way from MSb to LSb...same order we alloc EIRs */ @@ -283,7 +281,8 @@ void do_cpu_irq_mask(struct pt_regs *regs) __do_IRQ(irq, regs); } } - set_eiem(cpu_eiem); + + set_eiem(cpu_eiem); /* restore original mask */ irq_exit(); } -- 2.20.1