| Message ID | 1481113480-7663-1-git-send-email-julien.grall@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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@arm.com> > Link: https://lkml.org/lkml/2016/11/28/669 > Signed-off-by: Julien Grall <julien.grall@arm.com> > > Cc: stable@vger.kernel.org > > --- > > 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@kernel.org> 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 >
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;
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@arm.com> Link: https://lkml.org/lkml/2016/11/28/669 Signed-off-by: Julien Grall <julien.grall@arm.com> Cc: stable@vger.kernel.org --- I have requested backport to stable because the percpu allocator may misbehaves when the alignment is not a power of two. --- arch/arm/xen/enlighten.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)