On Sat, May 26, 2012 at 12:18:21PM +0200, Thomas Gleixner wrote: > On Fri, 25 May 2012, Suresh Siddha wrote: > > On Thu, 2012-05-24 at 21:16 +0200, Thomas Gleixner wrote: > > There are other (not-so common) irq desc references, like in the > > show_interrupts() (cat /proc/interrupts path) etc, that does things like > > this in the process context: > > > > desc = irq_to_desc(i); > > if (!desc) > > return 0; > > > > raw_spin_lock_irqsave(&desc->lock, flags); > > > > May be we should introduce something like > > get_irq_desc_locked()/put_irq_desc_locked() that can safely access the > > irq desc with pre-emption/irq's disabled and lock it etc. And the > > synchronize_sched() will enable the destroy_irq()/free_desc() to free it > > safely etc. > > I want to avoid that and instead use proper refcounting. The reason is > that we want to move the irq descriptor when the affinity changes > nodes, and for that we need refcounting anyway. >
While this proposal sounds good, in the meantime would there be any harm in putting the NULL cfg check into smp_irq_move_cleanup_interrupt()? It's a minimal change, and eliminates the panics that I've encountered thus far. Reposting the patch. A NULL pointer dereference can occur in smp_irq_move_cleanup_interrupt() if we haven't yet setup the irq_cfg pointer in the irq_desc.irq_data.chip_data. In create_irq_nr() there is a window where we have set vector_irq in __assign_irq_vector(), but not yet called irq_set_chip_data() to set the irq_cfg pointer. Should an IRQ_MOVE_CLEANUP_VECTOR hit the cpu in question during this time, smp_irq_move_cleanup_interrupt() will attempt to process the aforementioned irq, but panic when accessing irq_cfg. There is also a window in destroy_irq() where we've cleared the irq_cfg pointer in free_irq_cfg(), but have not yet called irq_free_desc(). Note that we have cleared vector_irq in __clear_irq_vector() prior to free_irq_cfg(), but smp_irq_move_cleanup_interrupt() might've already referenced the irq_desc. Only continue processing the irq if irq_cfg is non-NULL. Signed-off-by: Dimitri Sivanich <[email protected]> --- arch/x86/kernel/apic/io_apic.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) Index: linux/arch/x86/kernel/apic/io_apic.c =================================================================== --- linux.orig/arch/x86/kernel/apic/io_apic.c +++ linux/arch/x86/kernel/apic/io_apic.c @@ -2478,9 +2478,12 @@ asmlinkage void smp_irq_move_cleanup_int if (!desc) continue; - cfg = irq_cfg(irq); raw_spin_lock(&desc->lock); + cfg = irq_cfg(irq); + if (!cfg) + goto unlock; + /* * Check if the irq migration is in progress. If so, we * haven't received the cleanup request yet for this irq. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
