• Paul E. McKenney's avatar
    rcu: Correctly handle non-empty Tiny RCU callback list with none ready · d5ea436a
    Paul E. McKenney authored
    commit 6e91f8cb upstream.
    
    If, at the time __rcu_process_callbacks() is invoked,  there are callbacks
    in Tiny RCU's callback list, but none of them are ready to be invoked,
    the current list-management code will knit the non-ready callbacks out
    of the list.  This can result in hangs and possibly worse.  This commit
    therefore inserts a check for there being no callbacks that can be
    invoked immediately.
    
    This bug is unlikely to occur -- you have to get a new callback between
    the time rcu_sched_qs() or rcu_bh_qs() was called, but before we get to
    __rcu_process_callbacks().  It was detected by the addition of RCU-bh
    testing to rcutorture, which in turn was instigated by Iftekhar Ahmed's
    mutation testing.  Although this bug was made much more likely by
    915e8a4f (rcu: Remove fastpath from __rcu_process_callbacks()), this
    did not cause the bug, but rather made it much more probable.   That
    said, it takes more than 40 hours of rcutorture testing, on average,
    for this bug to appear, so this fix cannot be considered an emergency.
    Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
    [lizf: Backported to 3.4: adjust filename ]
    Signed-off-by: default avatarZefan Li <lizefan@huawei.com>
    d5ea436a
rcutiny.c 10.4 KB