From 46b0567c851cf85d6ba6f23eef385ec9111d09bc Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 15 Jun 2015 16:40:27 +0100 Subject: [PATCH] arm64: entry: fix context tracking for el0_sp_pc Commit 6c81fe7925cc4c42 ("arm64: enable context tracking") did not update el0_sp_pc to use ct_user_exit, but this appears to have been unintentional. In commit 6ab6463aeb5fbc75 ("arm64: adjust el0_sync so that a function can be called") we made x0 available, and in the return to userspace we call ct_user_enter in the kernel_exit macro. Due to this, we currently don't correctly inform RCU of the user->kernel transition, and may erroneously account for time spent in the kernel as if we were in an extended quiescent state when CONFIG_CONTEXT_TRACKING is enabled. As we do record the kernel->user transition, a userspace application making accesses from an unaligned stack pointer can demonstrate the imbalance, provoking the following warning: ------------[ cut here ]------------ WARNING: CPU: 2 PID: 3660 at kernel/context_tracking.c:75 context_tracking_enter+0xd8/0xe4() Modules linked in: CPU: 2 PID: 3660 Comm: a.out Not tainted 4.1.0-rc7+ #8 Hardware name: ARM Juno development board (r0) (DT) Call trace: [] dump_backtrace+0x0/0x124 [] show_stack+0x10/0x1c [] dump_stack+0x84/0xc8 [] warn_slowpath_common+0x98/0xd0 [] warn_slowpath_null+0x14/0x20 [] context_tracking_enter+0xd4/0xe4 [] preempt_schedule_irq+0xd4/0x114 [] el1_preempt+0x4/0x28 [] exit_files+0x38/0x4c [] do_exit+0x430/0x978 [] do_group_exit+0x40/0xd4 [] get_signal+0x23c/0x4f4 [] do_signal+0x1ac/0x518 [] do_notify_resume+0x5c/0x68 ---[ end trace 963c192600337066 ]--- This patch adds the missing ct_user_exit to the el0_sp_pc entry path, correcting the context tracking for this case. Signed-off-by: Mark Rutland Acked-by: Will Deacon Fixes: 6c81fe7925cc ("arm64: enable context tracking") Cc: # v3.17+ Signed-off-by: Catalin Marinas --- arch/arm64/kernel/entry.S | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 0eeb1b95c65a..a7691a378668 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -520,6 +520,7 @@ el0_sp_pc: mrs x26, far_el1 // enable interrupts before calling the main handler enable_dbg_and_irq + ct_user_exit mov x0, x26 mov x1, x25 mov x2, sp -- 2.11.0