On Wed, 7 Dec 2016, Julien Grall wrote: > The function xen_guest_init is using __alloc_percpu with an alignment > which are not power of two. > > However, the percpu allocator never supported alignments which are not power > of two and has always behaved incorectly in thise case. > > Commit 3ca45a4 "percpu: ensure requested alignment is power of two" > introduced a check which trigger a warning [1] when booting linux-next > on Xen. But in fine this bug was always present. > > This can be fixed by replacing the call to __alloc_percpu with > alloc_percpu. The latter will use an alignment which are a power of two. > > [1] > > [ 0.023921] illegal size (48) or align (48) for percpu allocation > [ 0.024167] ------------[ cut here ]------------ > [ 0.024344] WARNING: CPU: 0 PID: 1 at linux/mm/percpu.c:892 pcpu_alloc+0x88/0x6c0 > [ 0.024584] Modules linked in: > [ 0.024708] > [ 0.024804] CPU: 0 PID: 1 Comm: swapper/0 Not tainted > 4.9.0-rc7-next-20161128 #473 > [ 0.025012] Hardware name: Foundation-v8A (DT) > [ 0.025162] task: ffff80003d870000 task.stack: ffff80003d844000 > [ 0.025351] PC is at pcpu_alloc+0x88/0x6c0 > [ 0.025490] LR is at pcpu_alloc+0x88/0x6c0 > [ 0.025624] pc : [<ffff00000818e678>] lr : [<ffff00000818e678>] > pstate: 60000045 > [ 0.025830] sp : ffff80003d847cd0 > [ 0.025946] x29: ffff80003d847cd0 x28: 0000000000000000 > [ 0.026147] x27: 0000000000000000 x26: 0000000000000000 > [ 0.026348] x25: 0000000000000000 x24: 0000000000000000 > [ 0.026549] x23: 0000000000000000 x22: 00000000024000c0 > [ 0.026752] x21: ffff000008e97000 x20: 0000000000000000 > [ 0.026953] x19: 0000000000000030 x18: 0000000000000010 > [ 0.027155] x17: 0000000000000a3f x16: 00000000deadbeef > [ 0.027357] x15: 0000000000000006 x14: ffff000088f79c3f > [ 0.027573] x13: ffff000008f79c4d x12: 0000000000000041 > [ 0.027782] x11: 0000000000000006 x10: 0000000000000042 > [ 0.027995] x9 : ffff80003d847a40 x8 : 6f697461636f6c6c > [ 0.028208] x7 : 6120757063726570 x6 : ffff000008f79c84 > [ 0.028419] x5 : 0000000000000005 x4 : 0000000000000000 > [ 0.028628] x3 : 0000000000000000 x2 : 000000000000017f > [ 0.028840] x1 : ffff80003d870000 x0 : 0000000000000035 > [ 0.029056] > [ 0.029152] ---[ end trace 0000000000000000 ]--- > [ 0.029297] Call trace: > [ 0.029403] Exception stack(0xffff80003d847b00 to > 0xffff80003d847c30) > [ 0.029621] 7b00: 0000000000000030 0001000000000000 > ffff80003d847cd0 ffff00000818e678 > [ 0.029901] 7b20: 0000000000000002 0000000000000004 > ffff000008f7c060 0000000000000035 > [ 0.030153] 7b40: ffff000008f79000 ffff000008c4cd88 > ffff80003d847bf0 ffff000008101778 > [ 0.030402] 7b60: 0000000000000030 0000000000000000 > ffff000008e97000 00000000024000c0 > [ 0.030647] 7b80: 0000000000000000 0000000000000000 > 0000000000000000 0000000000000000 > [ 0.030895] 7ba0: 0000000000000035 ffff80003d870000 > 000000000000017f 0000000000000000 > [ 0.031144] 7bc0: 0000000000000000 0000000000000005 > ffff000008f79c84 6120757063726570 > [ 0.031394] 7be0: 6f697461636f6c6c ffff80003d847a40 > 0000000000000042 0000000000000006 > [ 0.031643] 7c00: 0000000000000041 ffff000008f79c4d > ffff000088f79c3f 0000000000000006 > [ 0.031877] 7c20: 00000000deadbeef 0000000000000a3f > [ 0.032051] [<ffff00000818e678>] pcpu_alloc+0x88/0x6c0 > [ 0.032229] [<ffff00000818ece8>] __alloc_percpu+0x18/0x20 > [ 0.032409] [<ffff000008d9606c>] xen_guest_init+0x174/0x2f4 > [ 0.032591] [<ffff0000080830f8>] do_one_initcall+0x38/0x130 > [ 0.032783] [<ffff000008d90c34>] kernel_init_freeable+0xe0/0x248 > [ 0.032995] [<ffff00000899a890>] kernel_init+0x10/0x100 > [ 0.033172] [<ffff000008082ec0>] ret_from_fork+0x10/0x50 > > Reported-by: Wei Chen <wei.chen@xxxxxxx> > Link: https://lkml.org/lkml/2016/11/28/669 > Signed-off-by: Julien Grall <julien.grall@xxxxxxx> > > Cc: stable@xxxxxxxxxxxxxxx > > --- > > I have requested backport to stable because the percpu allocator may > misbehaves when the alignment is not a power of two. Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx> I'll fix a small wording issue in the commit message and apply to xentip. > arch/arm/xen/enlighten.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c > index f193414..4986dc0 100644 > --- a/arch/arm/xen/enlighten.c > +++ b/arch/arm/xen/enlighten.c > @@ -372,8 +372,7 @@ static int __init xen_guest_init(void) > * for secondary CPUs as they are brought up. > * For uniformity we use VCPUOP_register_vcpu_info even on cpu0. > */ > - xen_vcpu_info = __alloc_percpu(sizeof(struct vcpu_info), > - sizeof(struct vcpu_info)); > + xen_vcpu_info = alloc_percpu(struct vcpu_info); > if (xen_vcpu_info == NULL) > return -ENOMEM; > > -- > 1.9.1 > -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html