Both a crash reported on freebsd-current on Oct. 18 under the
subject heading "mtx_lock() of destroyed mutex on NFS" and PR# 156168 appear to be caused by clnt_dg_destroy() closing down the socket prematurely. When to close down the socket is controlled by a reference count (cs_refs), but clnt_dg_create() checks for sb_upcall being non-NULL to decide if a new socket is needed. I believe the crashes were caused by the following race: clnt_dg_destroy() finds cs_refs == 0 and decides to delete socket clnt_dg_destroy() then loses race with clnt_dg_create() for acquisition of the SOCKBUF_LOCK() clnt_dg_create() finds sb_upcall != NULL and increments cs_refs to 1 clnt_dg_destroy() then acquires SOCKBUF_LOCK(), sets sb_upcall to NULL and destroys socket This patch fixes the above race by changing clnt_dg_destroy() so that it acquires SOCKBUF_LOCK() before testing cs_refs. Tested by: bz PR: 156168 Reviewed by: dfr MFC after: 2 weeks
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=227059
@ -1001,12 +1001,12 @@ clnt_dg_destroy(CLIENT *cl)
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cs = cu->cu_socket->so_rcv.sb_upcallarg;
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clnt_dg_close(cl);
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SOCKBUF_LOCK(&cu->cu_socket->so_rcv);
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mtx_lock(&cs->cs_lock);
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cs->cs_refs--;
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if (cs->cs_refs == 0) {
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mtx_unlock(&cs->cs_lock);
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SOCKBUF_LOCK(&cu->cu_socket->so_rcv);
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soupcall_clear(cu->cu_socket, SO_RCV);
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clnt_dg_upcallsdone(cu->cu_socket, cs);
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SOCKBUF_UNLOCK(&cu->cu_socket->so_rcv);
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@ -1015,6 +1015,7 @@ clnt_dg_destroy(CLIENT *cl)
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lastsocketref = TRUE;
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} else {
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mtx_unlock(&cs->cs_lock);
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SOCKBUF_UNLOCK(&cu->cu_socket->so_rcv);
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lastsocketref = FALSE;
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}
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