• Eric W. Biederman's avatar
    sysfs: Add lockdep annotations for the sysfs active reference · 846f9974
    Eric W. Biederman authored
    Holding locks over device_del -> kobject_del -> sysfs_deactivate can
    cause deadlocks if those same locks are grabbed in sysfs show or store
    methods.
    
    The I model s_active count + completion as a sleeping read/write lock.
    I describe to lockdep sysfs_get_active as a read_trylock,
    sysfs_put_active as a read_unlock, and sysfs_deactivate as a
    write_lock and write_unlock pair.  This seems to capture the essence
    for purposes of finding deadlocks, and in my testing gives finds real
    issues and ignores non-issues.
    
    This brings us back to holding locks over kobject_del is a problem
    that ideally we should find a way of addressing, but at least lockdep
    can tell us about the problems instead of requiring developers to debug
    rare strange system deadlocks, that happen when sysfs files are removed
    while being written to.
    Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
    Acked-by: default avatarTejun Heo <tj@kernel.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    846f9974
dir.c 20.4 KB