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If the INP lock is uncontested, avoid taking a reference and jumping

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through the lock-switching hoops.

A few of the INP lookup operations that lock INPs after the lookup do
so using this mechanism (to maintain lock ordering):

1. Lock lookup structure.
2. Find INP.
3. Acquire reference on INP.
4. Drop lock on lookup structure.
5. Acquire INP lock.
6. Drop reference on INP.

This change provides a slightly shorter path for cases where the INP
lock is uncontested:

1. Lock lookup structure.
2. Find INP.
3. Try to acquire the INP lock.
4. If successful, drop lock on lookup structure.

Of course, if the INP lock is contested, the functions will need to
revert to the previous way of switching locks safely.

This saves a few atomic operations when the INP lock is uncontested.

Discussed with:	gallatin, rrs, rwatson
MFC after:	2 weeks
Sponsored by:	Netflix, Inc.
Differential Revision:	https://reviews.freebsd.org/D12911
This commit is contained in:
Jonathan T. Looney 2018-03-21 15:54:46 +00:00
parent d614c09a82
commit 7fb2986ff6
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=331309
2 changed files with 104 additions and 44 deletions
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74
sys/netinet/in_pcb.c
View File

@ -1632,6 +1632,7 @@ in_pcblookup_group(struct inpcbinfo *pcbinfo, struct inpcbgroup *pcbgroup,
struct inpcbhead *head;
struct inpcb *inp, *tmpinp;
u_short fport = fport_arg, lport = lport_arg;
bool locked;
/*
* First look for an exact match.
@ -1818,18 +1819,32 @@ in_pcblookup_group(struct inpcbinfo *pcbinfo, struct inpcbgroup *pcbgroup,
return (NULL);
found:
in_pcbref(inp);
INP_GROUP_UNLOCK(pcbgroup);
if (lookupflags & INPLOOKUP_WLOCKPCB) {
INP_WLOCK(inp);
if (in_pcbrele_wlocked(inp))
return (NULL);
} else if (lookupflags & INPLOOKUP_RLOCKPCB) {
INP_RLOCK(inp);
if (in_pcbrele_rlocked(inp))
return (NULL);
} else
if (lookupflags & INPLOOKUP_WLOCKPCB)
locked = TRY_INP_WLOCK(inp);
else if (lookupflags & INPLOOKUP_RLOCKPCB)
locked = TRY_INP_RLOCK(inp);
else
panic("%s: locking bug", __func__);
if (!locked)
in_pcbref(inp);
INP_GROUP_UNLOCK(pcbgroup);
if (!locked) {
if (lookupflags & INPLOOKUP_WLOCKPCB) {
INP_WLOCK(inp);
if (in_pcbrele_wlocked(inp))
return (NULL);
} else {
INP_RLOCK(inp);
if (in_pcbrele_rlocked(inp))
return (NULL);
}
}
#ifdef INVARIANTS
if (lookupflags & INPLOOKUP_WLOCKPCB)
INP_WLOCK_ASSERT(inp);
else
INP_RLOCK_ASSERT(inp);
#endif
return (inp);
}
#endif /* PCBGROUP */
@ -1968,23 +1983,38 @@ in_pcblookup_hash(struct inpcbinfo *pcbinfo, struct in_addr faddr,
struct ifnet *ifp)
{
struct inpcb *inp;
bool locked;
INP_HASH_RLOCK(pcbinfo);
inp = in_pcblookup_hash_locked(pcbinfo, faddr, fport, laddr, lport,
(lookupflags & ~(INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB)), ifp);
if (inp != NULL) {
in_pcbref(inp);
INP_HASH_RUNLOCK(pcbinfo);
if (lookupflags & INPLOOKUP_WLOCKPCB) {
INP_WLOCK(inp);
if (in_pcbrele_wlocked(inp))
return (NULL);
} else if (lookupflags & INPLOOKUP_RLOCKPCB) {
INP_RLOCK(inp);
if (in_pcbrele_rlocked(inp))
return (NULL);
} else
if (lookupflags & INPLOOKUP_WLOCKPCB)
locked = INP_TRY_WLOCK(inp);
else if (lookupflags & INPLOOKUP_RLOCKPCB)
locked = INP_TRY_RLOCK(inp);
else
panic("%s: locking bug", __func__);
if (!locked)
in_pcbref(inp);
INP_HASH_RUNLOCK(pcbinfo);
if (!locked) {
if (lookupflags & INPLOOKUP_WLOCKPCB) {
INP_WLOCK(inp);
if (in_pcbrele_wlocked(inp))
return (NULL);
} else {
INP_RLOCK(inp);
if (in_pcbrele_rlocked(inp))
return (NULL);
}
}
#ifdef INVARIANTS
if (lookupflags & INPLOOKUP_WLOCKPCB)
INP_WLOCK_ASSERT(inp);
else
INP_RLOCK_ASSERT(inp);
#endif
} else
INP_HASH_RUNLOCK(pcbinfo);
return (inp);

74
sys/netinet6/in6_pcb.c
View File

@ -868,6 +868,7 @@ in6_pcblookup_group(struct inpcbinfo *pcbinfo, struct inpcbgroup *pcbgroup,
struct inpcbhead *head;
struct inpcb *inp, *tmpinp;
u_short fport = fport_arg, lport = lport_arg;
bool locked;
/*
* First look for an exact match.
@ -1026,18 +1027,32 @@ in6_pcblookup_group(struct inpcbinfo *pcbinfo, struct inpcbgroup *pcbgroup,
return (NULL);
found:
in_pcbref(inp);
INP_GROUP_UNLOCK(pcbgroup);
if (lookupflags & INPLOOKUP_WLOCKPCB) {
INP_WLOCK(inp);
if (in_pcbrele_wlocked(inp))
return (NULL);
} else if (lookupflags & INPLOOKUP_RLOCKPCB) {
INP_RLOCK(inp);
if (in_pcbrele_rlocked(inp))
return (NULL);
} else
if (lookupflags & INPLOOKUP_WLOCKPCB)
locked = INP_TRY_WLOCK(inp);
else if (lookupflags & INPLOOKUP_RLOCKPCB)
locked = INP_TRY_RLOCK(inp);
else
panic("%s: locking buf", __func__);
if (!locked)
in_pcbref(inp);
INP_GROUP_UNLOCK(pcbgroup);
if (!locked) {
if (lookupflags & INPLOOKUP_WLOCKPCB) {
INP_WLOCK(inp);
if (in_pcbrele_wlocked(inp))
return (NULL);
} else {
INP_RLOCK(inp);
if (in_pcbrele_rlocked(inp))
return (NULL);
}
}
#ifdef INVARIANTS
if (lookupflags & INPLOOKUP_WLOCKPCB)
INP_WLOCK_ASSERT(inp);
else
INP_RLOCK_ASSERT(inp);
#endif
return (inp);
}
#endif /* PCBGROUP */
@ -1163,23 +1178,38 @@ in6_pcblookup_hash(struct inpcbinfo *pcbinfo, struct in6_addr *faddr,
struct ifnet *ifp)
{
struct inpcb *inp;
bool locked;
INP_HASH_RLOCK(pcbinfo);
inp = in6_pcblookup_hash_locked(pcbinfo, faddr, fport, laddr, lport,
(lookupflags & ~(INPLOOKUP_RLOCKPCB | INPLOOKUP_WLOCKPCB)), ifp);
if (inp != NULL) {
in_pcbref(inp);
INP_HASH_RUNLOCK(pcbinfo);
if (lookupflags & INPLOOKUP_WLOCKPCB) {
INP_WLOCK(inp);
if (in_pcbrele_wlocked(inp))
return (NULL);
} else if (lookupflags & INPLOOKUP_RLOCKPCB) {
INP_RLOCK(inp);
if (in_pcbrele_rlocked(inp))
return (NULL);
} else
if (lookupflags & INPLOOKUP_WLOCKPCB)
locked = INP_TRY_WLOCK(inp);
else if (lookupflags & INPLOOKUP_RLOCKPCB)
locked = INP_TRY_RLOCK(inp);
else
panic("%s: locking bug", __func__);
if (!locked)
in_pcbref(inp);
INP_HASH_RUNLOCK(pcbinfo);
if (!locked) {
if (lookupflags & INPLOOKUP_WLOCKPCB) {
INP_WLOCK(inp);
if (in_pcbrele_wlocked(inp))
return (NULL);
} else {
INP_RLOCK(inp);
if (in_pcbrele_rlocked(inp))
return (NULL);
}
}
#ifdef INVARIANTS
if (lookupflags & INPLOOKUP_WLOCKPCB)
INP_WLOCK_ASSERT(inp);
else
INP_RLOCK_ASSERT(inp);
#endif
} else
INP_HASH_RUNLOCK(pcbinfo);
return (inp);