4.x mbuf binary compatibility; can it be broken?
dillon at apollo.backplane.com
Tue Jul 15 09:59:53 PDT 2003
:> How does it get 255+ references?
:I don't know exactly at this point. I can reproduce the situation at will
:with (in kernel) test code, but I don't know what exactly causes it in the
:Given that increasing the ref count limit is so easy, I was hoping to
:avoid spending time tracking down one degenerate case. :)
:Mike "Silby" Silbersack
It would be a good idea to make sure it isn't a runaway ref count.
I may be missing something, but I don't see how the ref count could
possibly reach 255 under any circumstances. mbufs using an mbuf
cluster (M_EXT with ext_ref == NULL) bump the ref count, and
duplicating an mbuf bumps the underlying cluster's ref count,
and splitting an mbuf bumps the ref count, and that is pretty much it.
Only m_copym() or m_copypacket() have any chance of legitimately
increasing the ref count beyond 255. Only a KASSERT() will tell us
who the likely candidate is. It could very well be that a ref count
is being lost somewhere.
More information about the freebsd-arch