• Jason Wessel's avatar
    kgdb,x86: do not set kgdb_single_step on x86 · 8097551d
    Jason Wessel authored
    On an SMP system the kgdb_single_step flag has the possibility to
    indefinitely hang the system in the case.  Consider the case where,
    CPU 1 has the schedule lock and CPU 0 is set to single step, there is
    no way for CPU 0 to run another task.
    
    The easy way to observe the problem is to make 2 cpus busy, and run
    the kgdb test suite.  You will see that it hangs the system very
    quickly.
    
    while [ 1 ] ; do find /proc > /dev/null 2>&1 ; done &
    while [ 1 ] ; do find /proc > /dev/null 2>&1 ; done &
    echo V1 > /sys/module/kgdbts/parameters/kgdbts
    
    The side effect of this patch is that there is the possibility
    to miss a breakpoint in the case that a single step operation
    was executed to step over a breakpoint in common code.
    
    The trade off of the missed breakpoint is preferred to
    hanging the kernel.  This can be fixed in the future by
    using kprobes or another strategy to step over planted
    breakpoints with out of line execution.
    
    CC: Ingo Molnar <mingo@elte.hu>
    Signed-off-by: default avatarJason Wessel <jason.wessel@windriver.com>
    8097551d
kgdb.c 15.7 KB