On 19/12/2012 2:31 PM, Vijay Singh wrote:
As it is today, a socket upcall on a listener socket is made with the
V_tcbinfo lock held. [tcp_input -> syncache_socket -> sonewconn ->
sowakeup].
I feel that the use of the V_tcbinfo is not consistent in the syncache code.
In syncache_add(), we drop the lock before doing the lookup:
INP_WUNLOCK(inp);
INP_INFO_WUNLOCK(&V_tcbinfo);
[..snip..]
sc = syncache_lookup(inc, &sch); /* returns locked entry */
However, when going through syncache_expand() or syncache_chkrst() we
keep the V_tcbinfo lock.
Since the syncache has its own lock, do we need to hold the V_tcbinfo
lock when calling syncache_socket()?
Every time the list of TCP control blocks (tcbinfo) is manipulated, a
write lock must be held to protect it. syncache_expand() is responsible
for 'expanding' the listening socket into a full blown accepted socket,
including creating its associated control block in the process.
By the way I don't think V_tcbinfo lock is held for syncache_chkrst() or
needed for that matter but I could be wrong since I'm looking at 7.x code.
Karim.
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