From d8550860d910c6b7b70f830f59003b33daaa52c9 Mon Sep 17 00:00:00 2001 From: Paul Burton Date: Fri, 3 Mar 2017 15:26:05 -0800 Subject: [PATCH] MIPS: Fix IRQ tracing & lockdep when rescheduling When the scheduler sets TIF_NEED_RESCHED & we call into the scheduler from arch/mips/kernel/entry.S we disable interrupts. This is true regardless of whether we reach work_resched from syscall_exit_work, resume_userspace or by looping after calling schedule(). Although we disable interrupts in these paths we don't call trace_hardirqs_off() before calling into C code which may acquire locks, and we therefore leave lockdep with an inconsistent view of whether interrupts are disabled or not when CONFIG_PROVE_LOCKING & CONFIG_DEBUG_LOCKDEP are both enabled. Without tracing this interrupt state lockdep will print warnings such as the following once a task returns from a syscall via syscall_exit_partial with TIF_NEED_RESCHED set: [ 49.927678] ------------[ cut here ]------------ [ 49.934445] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:3687 check_flags.part.41+0x1dc/0x1e8 [ 49.946031] DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled) [ 49.946355] CPU: 0 PID: 1 Comm: init Not tainted 4.10.0-00439-gc9fd5d362289-dirty #197 [ 49.963505] Stack : 0000000000000000 ffffffff81bb5d6a 0000000000000006 ffffffff801ce9c4 [ 49.974431] 0000000000000000 0000000000000000 0000000000000000 000000000000004a [ 49.985300] ffffffff80b7e487 ffffffff80a24498 a8000000ff160000 ffffffff80ede8b8 [ 49.996194] 0000000000000001 0000000000000000 0000000000000000 0000000077c8030c [ 50.007063] 000000007fd8a510 ffffffff801cd45c 0000000000000000 a8000000ff127c88 [ 50.017945] 0000000000000000 ffffffff801cf928 0000000000000001 ffffffff80a24498 [ 50.028827] 0000000000000000 0000000000000001 0000000000000000 0000000000000000 [ 50.039688] 0000000000000000 a8000000ff127bd0 0000000000000000 ffffffff805509bc [ 50.050575] 00000000140084e0 0000000000000000 0000000000000000 0000000000040a00 [ 50.061448] 0000000000000000 ffffffff8010e1b0 0000000000000000 ffffffff805509bc [ 50.072327] ... [ 50.076087] Call Trace: [ 50.079869] [] show_stack+0x80/0xa8 [ 50.086577] [] dump_stack+0x10c/0x190 [ 50.093498] [] __warn+0xf0/0x108 [ 50.099889] [] warn_slowpath_fmt+0x3c/0x48 [ 50.107241] [] check_flags.part.41+0x1dc/0x1e8 [ 50.114961] [] lock_is_held_type+0x8c/0xb0 [ 50.122291] [] __schedule+0x8c0/0x10f8 [ 50.129221] [] schedule+0x30/0x98 [ 50.135659] [] work_resched+0x8/0x34 [ 50.142397] ---[ end trace 0cb4f6ef5b99fe21 ]--- [ 50.148405] possible reason: unannotated irqs-off. [ 50.154600] irq event stamp: 400463 [ 50.159566] hardirqs last enabled at (400463): [] _raw_spin_unlock_irqrestore+0x40/0xa8 [ 50.171981] hardirqs last disabled at (400462): [] _raw_spin_lock_irqsave+0x30/0xb0 [ 50.183897] softirqs last enabled at (400450): [] __do_softirq+0x4ac/0x6a8 [ 50.195015] softirqs last disabled at (400425): [] irq_exit+0x110/0x128 Fix this by using the TRACE_IRQS_OFF macro to call trace_hardirqs_off() when CONFIG_TRACE_IRQFLAGS is enabled. This is done before invoking schedule() following the work_resched label because: 1) Interrupts are disabled regardless of the path we take to reach work_resched() & schedule(). 2) Performing the tracing here avoids the need to do it in paths which disable interrupts but don't call out to C code before hitting a path which uses the RESTORE_SOME macro that will call trace_hardirqs_on() or trace_hardirqs_off() as appropriate. We call trace_hardirqs_on() using the TRACE_IRQS_ON macro before calling syscall_trace_leave() for similar reasons, ensuring that lockdep has a consistent view of state after we re-enable interrupts. Signed-off-by: Paul Burton Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: linux-mips@linux-mips.org Cc: stable Patchwork: https://patchwork.linux-mips.org/patch/15385/ Signed-off-by: Ralf Baechle --- arch/mips/kernel/entry.S | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S index 8d83fc2a96b7..38a302919e6b 100644 --- a/arch/mips/kernel/entry.S +++ b/arch/mips/kernel/entry.S @@ -11,6 +11,7 @@ #include #include #include +#include #include #include #include @@ -119,6 +120,7 @@ work_pending: andi t0, a2, _TIF_NEED_RESCHED # a2 is preloaded with TI_FLAGS beqz t0, work_notifysig work_resched: + TRACE_IRQS_OFF jal schedule local_irq_disable # make sure need_resched and @@ -155,6 +157,7 @@ syscall_exit_work: beqz t0, work_pending # trace bit set? local_irq_enable # could let syscall_trace_leave() # call schedule() instead + TRACE_IRQS_ON move a0, sp jal syscall_trace_leave b resume_userspace -- 2.20.1