On Fri, 28 Sep 2007 10:52:08 +0200 Laurent Vivier <[EMAIL PROTECTED]> wrote:
> Fengguang Wu wrote: > > On Thu, Sep 27, 2007 at 02:22:20AM -0700, Andrew Morton wrote: > >> ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.23-rc8/2.6.23-rc8-mm2/ > > > > Laurent, > > > > It triggered a WARNING on first run in qemu: > > Thank you to report it. > > > > > [ 0.310000] WARNING: at arch/x86_64/kernel/smp.c:397 > > smp_call_function_mask() > > [ 0.310000] > > [ 0.310000] Call Trace: > > [ 0.310000] [<ffffffff8100dbde>] dump_trace+0x3ee/0x4a0 > > [ 0.310000] [<ffffffff8100dcd3>] show_trace+0x43/0x70 > > [ 0.310000] [<ffffffff8100dd15>] dump_stack+0x15/0x20 > > [ 0.310000] [<ffffffff8101cd44>] smp_call_function_mask+0x94/0xa0 > > [ 0.310000] [<ffffffff8101cd69>] smp_call_function+0x19/0x20 > > [ 0.310000] [<ffffffff8104277f>] on_each_cpu+0x1f/0x50 > > [ 0.310000] [<ffffffff81026eac>] global_flush_tlb+0x8c/0x110 > > [ 0.310000] [<ffffffff81025c85>] free_init_pages+0xe5/0xf0 > > [ 0.310000] [<ffffffff81549b5e>] alternative_instructions+0x7e/0x150 > > [ 0.310000] [<ffffffff8154a2ea>] check_bugs+0x1a/0x20 > > [ 0.310000] [<ffffffff81540c4a>] start_kernel+0x2da/0x380 > > [ 0.310000] [<ffffffff81540132>] _sinittext+0x132/0x140 > > > the reason is the WARN_ON(): > > 390 int smp_call_function_mask(cpumask_t mask, > 391 void (*func)(void *), void *info, > 392 int wait) > 393 { > 394 int ret; > 395 > 396 /* Can deadlock when called with interrupts disabled */ > 397 WARN_ON(irqs_disabled()); > 398 > 399 spin_lock(&call_lock); > 400 ret = __smp_call_function_mask(mask, func, info, wait); > 401 spin_unlock(&call_lock); > 402 return ret; > 403 } > > The patch I sent to Andi didn't include this WARN_ON() and it's why I didn't > find this issue. (see http://lkml.org/lkml/2007/8/24/101) > > smp_call_function_mask() is called by smp_call_function() which calls a > function > on all CPU except current. > The comment of smp_call_function() specifies: > ... > * You must not call this function with disabled interrupts or from a > * hardware interrupt handler or from a bottom half handler. > * Actually there are a few legal cases, like panic. > */ > > So this WARN_ON() is correct, and the caller (global_flush_tlb()) doesn't > follow > this rule. > > I guess this WARN_ON() is only needed when we have current CPU in provided > mask. > So I think we should change: > > int smp_call_function (void (*func) (void *info), void *info, int nonatomic, > int wait) > { > return smp_call_function_mask(cpu_online_map, func, info, wait); > } > ("cpu_online_map" is a bad choice, comment also specifies: "run a function on > all other CPU") > > to > > int smp_call_function (void (*func) (void *info), void *info, int nonatomic, > int wait) > { > int ret; > cpumask_t allbutself; > > allbutself = cpu_online_map; > cpu_clear(smp_processor_id(), allbutself); > > spin_lock(&call_lock); > ret = __smp_call_function_mask(allbutself, func, info, wait); > spin_unlock(&call_lock); > return ret; > } > (which is smp_call_function_mask() without the WARN_ON() and without current > cpu > in the mask) > > Andi, is this correct ? > Andrew, should I send a patch implementing this change ? umm, I think all the smp_call_function fucntions are deadlocky if called with local interrupts disabled, regardless of whether the calling CPU is in the mask. If CPU A is sending a cross-cpu call to CPU B and CPU B is sending a cross-cpu call to CPU A, and they both have local interrupts disabled... - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/