• Jonathan Corbet's avatar
    Move FASYNC bit handling to f_op->fasync() · 76398425
    Jonathan Corbet authored
    Removing the BKL from FASYNC handling ran into the challenge of keeping the
    setting of the FASYNC bit in filp->f_flags atomic with regard to calls to
    the underlying fasync() function.  Andi Kleen suggested moving the handling
    of that bit into fasync(); this patch does exactly that.  As a result, we
    have a couple of internal API changes: fasync() must now manage the FASYNC
    bit, and it will be called without the BKL held.
    As it happens, every fasync() implementation in the kernel with one
    exception calls fasync_helper().  So, if we make fasync_helper() set the
    FASYNC bit, we can avoid making any changes to the other fasync()
    functions - as long as those functions, themselves, have proper locking.
    Most fasync() implementations do nothing but call fasync_helper() - which
    has its own lock - so they are easily verified as correct.  The BKL had
    already been pushed down into the rest.
    The networking code has its own version of fasync_helper(), so that code
    has been augmented with explicit FASYNC bit handling.
    Cc: Al Viro <viro@ZenIV.linux.org.uk>
    Cc: David Miller <davem@davemloft.net>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
ioctl.c 13.7 KB