• Thomas Gleixner's avatar
    genirq/proc: Reject invalid affinity masks (again) · cba6437a
    Thomas Gleixner authored
    Qian Cai reported that the WARN_ON() in the x86/msi affinity setting code,
    which catches cases where the affinity setting is not done on the CPU which
    is the current target of the interrupt, triggers during CPU hotplug stress
    testing.
    
    It turns out that the warning which was added with the commit addressing
    the MSI affinity race unearthed yet another long standing bug.
    
    If user space writes a bogus affinity mask, i.e. it contains no online CPUs,
    then it calls irq_select_affinity_usr(). This was introduced for ALPHA in
    
      eee45269 ("[PATCH] Alpha: convert to generic irq framework (generic part)")
    
    and subsequently made available for all architectures in
    
      18404756 ("genirq: Expose default irq affinity mask (take 3)")
    
    which introduced the circumvention of the affinity setting restrictions for
    interrupt which cannot be moved in process context.
    
    The whole exercise is bogus in various aspects:
    
      1) If the interrupt is already started up then there is absolutely
         no point to honour a bogus interrupt affinity setting from user
         space. The interrupt is already assigned to an online CPU and it
         does not make any sense to reassign it to some other randomly
         chosen online CPU.
    
      2) If the interupt is not yet started up then there is no point
         either. A subsequent startup of the interrupt will invoke
         irq_setup_affinity() anyway which will chose a valid target CPU.
    
    So the only correct solution is to just return -EINVAL in case user space
    wrote an affinity mask which does not contain any online CPUs, except for
    ALPHA which has it's own magic sauce for this.
    
    Fixes: 18404756 ("genirq: Expose default irq affinity mask (take 3)")
    Reported-by: default avatarQian Cai <cai@lca.pw>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Tested-by: default avatarQian Cai <cai@lca.pw>
    Link: https://lkml.kernel.org/r/878sl8xdbm.fsf@nanos.tec.linutronix.de
    
    cba6437a
internals.h 13.9 KB