On Thu, 8 Feb 2007 17:07:28 +0800 "Cong WANG" <[EMAIL PROTECTED]> wrote:
> Kfifo is a ring-buffer in kernel which can be used as a lock-free way > for concurrent read/write when there are only one producer and one > consumer. Details of its design can be found in kernel/kfifo.c and > include/linux/kfifo.h. > > You will find that the 'in' and 'out' fields of 'struct kfifo' are > both represented as 'unsigned int' and in most cases 'in' is larger > than 'out' and their difference will NOT be over 'size'. > > Now the problem is that 'in' will be *smaller* than 'out' when 'in' > overflows and 'out' doesn't (Yes, this may occur quietly.). This is > NOT what we expect, though it may not cause any serious problems if we > carefully use kfifo*() functions. And this is really a bug. You seem to be saying that it's not a bug, but it's a bug. Exactly what goes wrong? > This bug > affects the kernel since version 2.6.10. I have tested this patch on > x86 machines. > > Signed-off-by: WANG Cong <[EMAIL PROTECTED]> > > --- > > --- kernel/kfifo.c.orig 2007-02-07 19:42:51.000000000 +0800 > +++ kernel/kfifo.c 2007-02-07 19:43:31.000000000 +0800 > @@ -24,6 +24,7 @@ > #include <linux/slab.h> > #include <linux/err.h> > #include <linux/kfifo.h> > +#include <linux/compiler.h> > > /** > * kfifo_init - allocates a new FIFO using a preallocated buffer > @@ -120,6 +121,12 @@ unsigned int __kfifo_put(struct kfifo *f > { > unsigned int l; > > + /*If only fifo->in overflows, let both overflow!*/ > + if (unlikely(fifo->in < fifo->out)) { > + fifo->out += fifo->size; > + fifo->in += fifo->size; > + } > + hm. That would indicate that there's a problem elsewhere in the logic. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/