• Thomas Gleixner's avatar
    hotplug: Prevent alloc/free of irq descriptors during cpu up/down · a8994181
    Thomas Gleixner authored
    When a cpu goes up some architectures (e.g. x86) have to walk the irq
    space to set up the vector space for the cpu. While this needs extra
    protection at the architecture level we can avoid a few race
    conditions by preventing the concurrent allocation/free of irq
    descriptors and the associated data.
    
    When a cpu goes down it moves the interrupts which are targeted to
    this cpu away by reassigning the affinities. While this happens
    interrupts can be allocated and freed, which opens a can of race
    conditions in the code which reassignes the affinities because
    interrupt descriptors might be freed underneath.
    
    Example:
    
    CPU1				CPU2
    cpu_up/down
     irq_desc = irq_to_desc(irq);
    				remove_from_radix_tree(desc);
     raw_spin_lock(&desc->lock);
    				free(desc);
    
    We could protect the irq descriptors with RCU, but that would require
    a full tree change of all accesses to interrupt descriptors. But
    fortunately these kind of race conditions are rather limited to a few
    things like cpu hotplug. The normal setup/teardown is very well
    serialized. So the simpler and obvious solution is:
    
    Prevent allocation and freeing of interrupt descriptors accross cpu
    hotplug.
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
    Cc: xiao jin <jin.xiao@intel.com>
    Cc: Joerg Roedel <jroedel@suse.de>
    Cc: Borislav Petkov <bp@suse.de>
    Cc: Yanmin Zhang <yanmin_zhang@linux.intel.com>
    Link: http://lkml.kernel.org/r/20150705171102.063519515@linutronix.de
    a8994181
internals.h 6.52 KB