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authordfr <dfr@FreeBSD.org>2008-07-23 09:18:08 +0000
committerdfr <dfr@FreeBSD.org>2008-07-23 09:18:08 +0000
commitd27f65928a6e40f7d6391c4441edc752c1702212 (patch)
tree028a6d06e3b062550f56b8bed3425803c2aad92f /sys/rpc
parent42aeaf36b0bea599f34b9841feaa487a33e73f4b (diff)
downloadFreeBSD-src-d27f65928a6e40f7d6391c4441edc752c1702212.zip
FreeBSD-src-d27f65928a6e40f7d6391c4441edc752c1702212.tar.gz
Re-work the code slightly to avoid a possible livelock.
MFC after: 2 weeks
Diffstat (limited to 'sys/rpc')
-rw-r--r--sys/rpc/auth_unix.c50
1 files changed, 27 insertions, 23 deletions
diff --git a/sys/rpc/auth_unix.c b/sys/rpc/auth_unix.c
index 28e07f8..e30e59e 100644
--- a/sys/rpc/auth_unix.c
+++ b/sys/rpc/auth_unix.c
@@ -55,6 +55,7 @@ __FBSDID("$FreeBSD$");
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/pcpu.h>
+#include <sys/refcount.h>
#include <sys/sx.h>
#include <sys/ucred.h>
@@ -86,7 +87,7 @@ static struct auth_ops authunix_ops = {
struct audata {
TAILQ_ENTRY(audata) au_link;
TAILQ_ENTRY(audata) au_alllink;
- int au_refs;
+ volatile u_int au_refs;
struct xucred au_xcred;
struct opaque_auth au_origcred; /* original credentials */
struct opaque_auth au_shcred; /* short hand cred */
@@ -157,6 +158,7 @@ again:
sx_slock(&auth_unix_lock);
TAILQ_FOREACH(au, &auth_unix_cache[h], au_link) {
if (!memcmp(&xcr, &au->au_xcred, sizeof(xcr))) {
+ refcount_acquire(&au->au_refs);
if (sx_try_upgrade(&auth_unix_lock)) {
/*
* Keep auth_unix_all LRU sorted.
@@ -164,16 +166,16 @@ again:
TAILQ_REMOVE(&auth_unix_all, au, au_alllink);
TAILQ_INSERT_TAIL(&auth_unix_all, au,
au_alllink);
- au->au_refs++;
sx_xunlock(&auth_unix_lock);
- return (au->au_auth);
} else {
sx_sunlock(&auth_unix_lock);
- goto again;
}
+ return (au->au_auth);
}
}
+ sx_sunlock(&auth_unix_lock);
+
/*
* Allocate and set up auth handle
*/
@@ -183,7 +185,7 @@ again:
auth->ah_ops = &authunix_ops;
auth->ah_private = (caddr_t)au;
auth->ah_verf = au->au_shcred = _null_auth;
- au->au_refs = 1;
+ refcount_init(&au->au_refs, 1);
au->au_xcred = xcr;
au->au_shfaults = 0;
au->au_origcred.oa_base = NULL;
@@ -210,18 +212,26 @@ again:
auth->ah_cred = au->au_origcred;
marshal_new_auth(auth);
- if (sx_try_upgrade(&auth_unix_lock)) {
- auth_unix_count++;
- TAILQ_INSERT_TAIL(&auth_unix_cache[h], au, au_link);
- TAILQ_INSERT_TAIL(&auth_unix_all, au, au_alllink);
- au->au_refs++; /* one for the cache, one for user */
- sx_xunlock(&auth_unix_lock);
- return (auth);
- } else {
- sx_sunlock(&auth_unix_lock);
- AUTH_DESTROY(auth);
- goto again;
+ sx_xlock(&auth_unix_lock);
+ TAILQ_FOREACH(tau, &auth_unix_cache[h], au_link) {
+ if (!memcmp(&xcr, &tau->au_xcred, sizeof(xcr))) {
+ /*
+ * We lost a race to create the AUTH that
+ * matches this cred.
+ */
+ sx_xunlock(&auth_unix_lock);
+ AUTH_DESTROY(auth);
+ goto again;
+ }
}
+
+ auth_unix_count++;
+ TAILQ_INSERT_TAIL(&auth_unix_cache[h], au, au_link);
+ TAILQ_INSERT_TAIL(&auth_unix_all, au, au_alllink);
+ refcount_acquire(&au->au_refs); /* one for the cache, one for user */
+ sx_xunlock(&auth_unix_lock);
+
+ return (auth);
}
/*
@@ -316,16 +326,10 @@ static void
authunix_destroy(AUTH *auth)
{
struct audata *au;
- int refs;
au = AUTH_PRIVATE(auth);
- sx_xlock(&auth_unix_lock);
- au->au_refs--;
- refs = au->au_refs;
- sx_xunlock(&auth_unix_lock);
-
- if (refs > 0)
+ if (!refcount_release(&au->au_refs))
return;
mem_free(au->au_origcred.oa_base, au->au_origcred.oa_length);
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