• Paul Burton's avatar
    MIPS: Fix IRQ tracing & lockdep when rescheduling · 392bd6b1
    Paul Burton authored
    commit d8550860 upstream.
    
    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] [<ffffffff8010e1b0>] show_stack+0x80/0xa8
    [   50.086577] [<ffffffff805509bc>] dump_stack+0x10c/0x190
    [   50.093498] [<ffffffff8015dde0>] __warn+0xf0/0x108
    [   50.099889] [<ffffffff8015de34>] warn_slowpath_fmt+0x3c/0x48
    [   50.107241] [<ffffffff801c15b4>] check_flags.part.41+0x1dc/0x1e8
    [   50.114961] [<ffffffff801c239c>] lock_is_held_type+0x8c/0xb0
    [   50.122291] [<ffffffff809461b8>] __schedule+0x8c0/0x10f8
    [   50.129221] [<ffffffff80946a60>] schedule+0x30/0x98
    [   50.135659] [<ffffffff80106278>] 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): [<ffffffff8094edc8>] _raw_spin_unlock_irqrestore+0x40/0xa8
    [   50.171981] hardirqs last disabled at (400462): [<ffffffff8094eb98>] _raw_spin_lock_irqsave+0x30/0xb0
    [   50.183897] softirqs last  enabled at (400450): [<ffffffff8016580c>] __do_softirq+0x4ac/0x6a8
    [   50.195015] softirqs last disabled at (400425): [<ffffffff80165e78>] 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: default avatarPaul Burton <paul.burton@imgtec.com>
    Fixes: 1da177e4 ("Linux-2.6.12-rc2")
    Cc: linux-mips@linux-mips.org
    Patchwork: https://patchwork.linux-mips.org/patch/15385/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
    [bwh: Backported to 3.2: adjust context]
    Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
    392bd6b1
entry.S 4.47 KB