• Steven Rostedt (Red Hat)'s avatar
    trace,x86: Do not call local_irq_save() in load_current_idt() · 2b4bc789
    Steven Rostedt (Red Hat) authored
    As load_current_idt() is now what is used to update the IDT for the
    switches needed for NMI, lockdep debug, and for tracing, it must not
    call local_irq_save(). This is because one of the users of this is
    lockdep, which does tracing of local_irq_save() and when the debug
    trap is hit, we need to update the IDT before tracing interrupts
    being disabled. As load_current_idt() is used to do this, calling
    local_irq_save() which lockdep traces, defeats the point of calling
    load_current_idt().
    
    As interrupts are already disabled when used by lockdep and NMI, the
    only other user is tracing that can disable interrupts itself. Simply
    have the tracing update disable interrupts before calling load_current_idt()
    instead of breaking the other users.
    
    Here's the dump that happened:
    
    ------------[ cut here ]------------
    WARNING: at /work/autotest/nobackup/linux-test.git/kernel/fork.c:1196 copy_process+0x2c3/0x1398()
    DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled)
    Modules linked in:
    CPU: 1 PID: 4570 Comm: gdm-simple-gree Not tainted 3.10.0-rc3-test+ #5
    Hardware name:                  /DG965MQ, BIOS MQ96510J.86A.0372.2006.0605.1717 06/05/2006
     ffffffff81d2a7a5 ffff88006ed13d50 ffffffff8192822b ffff88006ed13d90
     ffffffff81035f25 ffff8800721c6000 ffff88006ed13da0 0000000001200011
     0000000000000000 ffff88006ed5e000 ffff8800721c6000 ffff88006ed13df0
    Call Trace:
     [<ffffffff8192822b>] dump_stack+0x19/0x1b
     [<ffffffff81035f25>] warn_slowpath_common+0x67/0x80
     [<ffffffff81035fe1>] warn_slowpath_fmt+0x46/0x48
     [<ffffffff812bfc5d>] ? __raw_spin_lock_init+0x31/0x52
     [<ffffffff810341f7>] copy_process+0x2c3/0x1398
     [<ffffffff8103539d>] do_fork+0xa8/0x260
     [<ffffffff810ca7b1>] ? trace_preempt_on+0x2a/0x2f
     [<ffffffff812afb3e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
     [<ffffffff81937fe7>] ? sysret_check+0x1b/0x56
     [<ffffffff81937fe7>] ? sysret_check+0x1b/0x56
     [<ffffffff810355cf>] SyS_clone+0x16/0x18
     [<ffffffff81938369>] stub_clone+0x69/0x90
     [<ffffffff81937fc2>] ? system_call_fastpath+0x16/0x1b
    ---[ end trace 8b157a9d20ca1aa2 ]---
    
    in fork.c:
    
     #ifdef CONFIG_PROVE_LOCKING
    	DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled); <-- bug here
    	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
     #endif
    
    Cc: Seiji Aguchi <seiji.aguchi@hds.com>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    2b4bc789
tracepoint.c 1.29 KB