Date: Wed, 13 Jun 2001 10:37:22 -0700 (PDT) From: Matthew Jacob <mjacob@feral.com> To: freebsd-current@freebsd.org Subject: MBUF locking- this can't be right, can it? Message-ID: <Pine.BSF.4.21.0106131033130.40934-100000@beppo.feral.com>
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A recent change to the MFREE macro was made as noted below:
/*
* MFREE(struct mbuf *m, struct mbuf *n)
* Free a single mbuf and associated external storage.
* Place the successor, if any, in n.
*
* we do need to check non-first mbuf for m_aux, since some of existing
* code does not call M_PREPEND properly.
* (example: call to bpf_mtap from drivers)
*/
#define MFREE(m, n) do { \
struct mbuf *_mm = (m); \
\
KASSERT(_mm->m_type != MT_FREE, ("freeing free mbuf")); \
if (_mm->m_flags & M_EXT) \
MEXTFREE(_mm); \
mtx_lock(&mbuf_mtx); \
mbtypes[_mm->m_type]--; \
++ if ((_mm->m_flags & M_PKTHDR) != 0 && _mm->m_pkthdr.aux) { \
++ m_freem(_mm->m_pkthdr.aux); \
++ _mm->m_pkthdr.aux = NULL; \
++ } \
_mm->m_type = MT_FREE; \
mbtypes[MT_FREE]++; \
(n) = _mm->m_next; \
_mm->m_next = mmbfree.m_head; \
mmbfree.m_head = _mm; \
MBWAKEUP(m_mballoc_wid, &mmbfree.m_starved); \
mtx_unlock(&mbuf_mtx); \
} while (0)
Unfortunately, m_freem also calls MFREE. Tsk. Now, it seems to me that even in
cases where you *could* allow recursive locks, the right idea here would be to
change it to:
/*
* MFREE(struct mbuf *m, struct mbuf *n)
* Free a single mbuf and associated external storage.
* Place the successor, if any, in n.
*
* we do need to check non-first mbuf for m_aux, since some of existing
* code does not call M_PREPEND properly.
* (example: call to bpf_mtap from drivers)
*/
#define MFREE(m, n) do { \
struct mbuf *_mm = (m); \
struct mbuf *_aux; \
\
KASSERT(_mm->m_type != MT_FREE, ("freeing free mbuf")); \
if (_mm->m_flags & M_EXT) \
MEXTFREE(_mm); \
mtx_lock(&mbuf_mtx); \
mbtypes[_mm->m_type]--; \
if ((_mm->m_flags & M_PKTHDR) != 0 && _mm->m_pkthdr.aux) { \
_aux = _mm->m_pkthdr.aux; \
_mm->m_pkthdr.aux = NULL; \
} else { \
_aux = NULL; \
} \
_mm->m_type = MT_FREE; \
mbtypes[MT_FREE]++; \
(n) = _mm->m_next; \
_mm->m_next = mmbfree.m_head; \
mmbfree.m_head = _mm; \
MBWAKEUP(m_mballoc_wid, &mmbfree.m_starved); \
mtx_unlock(&mbuf_mtx); \
if (_aux) \
m_freem(_aux); \
} while (0)
Comments?
-matt
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