[PATCH 3/3] qemu_capabilities: Reword domain caps cache
Michal Privoznik
mprivozn at redhat.com
Fri Jan 24 10:27:18 UTC 2020
Since v5.6.0-48-g270583ed98 we try to cache domain capabilities,
i.e. store filled virDomainCaps in a hash table in virQEMUCaps
for future use. However, there's a race condition in the way it's
implemented. We use virQEMUCapsGetDomainCapsCache() to obtain the
pointer to the hash table, then we search the hash table for
cached data and if none is found the domcaps is constructed and
put into the table. Problem is that this is all done without any
locking, so if there are two threads trying to do the same, one
will succeed and the other will fail inserting the data into the
table.
Also, the API looks a bit fishy - obtaining pointer to the hash
table is dangerous.
The solution is to use a mutex that guards the whole operation
with the hash table. Then, the API can be changes to return
virDomainCapsPtr directly.
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1791790
Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
src/qemu/qemu_capabilities.c | 118 +++++++++++++++++++++++++++++++++--
src/qemu/qemu_capabilities.h | 14 ++++-
src/qemu/qemu_conf.c | 69 +++++---------------
3 files changed, 141 insertions(+), 60 deletions(-)
diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 17b0134ab8..ef3bfb7093 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -598,6 +598,26 @@ struct _virQEMUCapsAccel {
qemuMonitorCPUDefsPtr cpuModels;
};
+
+typedef struct _virQEMUDomainCapsCache virQEMUDomainCapsCache;
+typedef virQEMUDomainCapsCache *virQEMUDomainCapsCachePtr;
+struct _virQEMUDomainCapsCache {
+ virObjectLockable parent;
+
+ virHashTablePtr cache;
+};
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(virQEMUDomainCapsCache, virObjectUnref);
+
+static virClassPtr virQEMUDomainCapsCacheClass;
+static void virQEMUDomainCapsCacheDispose(void *obj)
+{
+ virQEMUDomainCapsCachePtr cache = obj;
+
+ virHashFree(cache->cache);
+}
+
+
/*
* Update the XML parser/formatter when adding more
* information to this struct so that it gets cached
@@ -629,7 +649,7 @@ struct _virQEMUCaps {
virArch arch;
- virHashTablePtr domCapsCache;
+ virQEMUDomainCapsCachePtr domCapsCache;
size_t ngicCapabilities;
virGICCapability *gicCapabilities;
@@ -655,6 +675,9 @@ static int virQEMUCapsOnceInit(void)
if (!VIR_CLASS_NEW(virQEMUCaps, virClassForObject()))
return -1;
+ if (!(VIR_CLASS_NEW(virQEMUDomainCapsCache, virClassForObjectLockable())))
+ return -1;
+
return 0;
}
@@ -1625,6 +1648,22 @@ int virQEMUCapsGetDefaultVersion(virCapsPtr caps,
}
+static virQEMUDomainCapsCachePtr
+virQEMUDomainCapsCacheNew(void)
+{
+ g_autoptr(virQEMUDomainCapsCache) cache = NULL;
+
+ if (virQEMUCapsInitialize() < 0)
+ return NULL;
+
+ if (!(cache = virObjectLockableNew(virQEMUDomainCapsCacheClass)))
+ return NULL;
+
+ if (!(cache->cache = virHashCreate(5, virObjectFreeHashData)))
+ return NULL;
+
+ return g_steal_pointer(&cache);
+}
virQEMUCapsPtr
@@ -1642,7 +1681,7 @@ virQEMUCapsNew(void)
if (!(qemuCaps->flags = virBitmapNew(QEMU_CAPS_LAST)))
goto error;
- if (!(qemuCaps->domCapsCache = virHashCreate(5, virObjectFreeHashData)))
+ if (!(qemuCaps->domCapsCache = virQEMUDomainCapsCacheNew()))
goto error;
return qemuCaps;
@@ -1832,7 +1871,7 @@ void virQEMUCapsDispose(void *obj)
{
virQEMUCapsPtr qemuCaps = obj;
- virHashFree(qemuCaps->domCapsCache);
+ virObjectUnref(qemuCaps->domCapsCache);
virBitmapFree(qemuCaps->flags);
VIR_FREE(qemuCaps->package);
@@ -1992,9 +2031,78 @@ const char *virQEMUCapsGetPackage(virQEMUCapsPtr qemuCaps)
}
-virHashTablePtr virQEMUCapsGetDomainCapsCache(virQEMUCapsPtr qemuCaps)
+struct virQEMUCapsSearchDomcapsData {
+ const char *path;
+ const char *machine;
+ virArch arch;
+ virDomainVirtType virttype;
+};
+
+
+static int
+virQEMUCapsSearchDomcaps(const void *payload,
+ const void *name G_GNUC_UNUSED,
+ const void *opaque)
{
- return qemuCaps->domCapsCache;
+ virDomainCapsPtr domCaps = (virDomainCapsPtr) payload;
+ struct virQEMUCapsSearchDomcapsData *data = (struct virQEMUCapsSearchDomcapsData *) opaque;
+
+ if (STREQ_NULLABLE(data->path, domCaps->path) &&
+ STREQ_NULLABLE(data->machine, domCaps->machine) &&
+ data->arch == domCaps->arch &&
+ data->virttype == domCaps->virttype)
+ return 1;
+
+ return 0;
+}
+
+virDomainCapsPtr
+virQEMUCapsGetDomainCapsCache(virQEMUCapsPtr qemuCaps,
+ const char *machine,
+ virArch arch,
+ virDomainVirtType virttype,
+ virQEMUCapsGetDomainCapsCacheFiller fillDomainCaps,
+ void *opaque)
+{
+ virQEMUDomainCapsCachePtr cache = qemuCaps->domCapsCache;
+ virDomainCapsPtr domCaps = NULL;
+ const char *path = virQEMUCapsGetBinary(qemuCaps);
+ struct virQEMUCapsSearchDomcapsData data = {
+ .path = path,
+ .machine = machine,
+ .arch = arch,
+ .virttype = virttype,
+ };
+
+ virObjectLock(cache);
+
+ domCaps = virHashSearch(cache->cache, virQEMUCapsSearchDomcaps, &data, NULL);
+
+ if (!domCaps) {
+ g_autoptr(virDomainCaps) tempDomCaps = NULL;
+ g_autofree char *key = NULL;
+
+ /* hash miss, build new domcaps */
+ if (!(tempDomCaps = virDomainCapsNew(path, machine,
+ arch, virttype)))
+ goto cleanup;
+
+ if ((fillDomainCaps)(tempDomCaps, qemuCaps, opaque) < 0)
+ goto cleanup;
+
+ key = g_strdup_printf("%d:%d:%s:%s", arch, virttype,
+ NULLSTR(machine), path);
+
+ if (virHashAddEntry(cache->cache, key, tempDomCaps) < 0)
+ goto cleanup;
+
+ domCaps = g_steal_pointer(&tempDomCaps);
+ }
+
+ virObjectRef(domCaps);
+ cleanup:
+ virObjectUnlock(cache);
+ return domCaps;
}
diff --git a/src/qemu/qemu_capabilities.h b/src/qemu/qemu_capabilities.h
index ebfdb4b981..395d4afaee 100644
--- a/src/qemu/qemu_capabilities.h
+++ b/src/qemu/qemu_capabilities.h
@@ -575,7 +575,19 @@ const char *virQEMUCapsGetBinary(virQEMUCapsPtr qemuCaps);
virArch virQEMUCapsGetArch(virQEMUCapsPtr qemuCaps);
unsigned int virQEMUCapsGetVersion(virQEMUCapsPtr qemuCaps);
const char *virQEMUCapsGetPackage(virQEMUCapsPtr qemuCaps);
-virHashTablePtr virQEMUCapsGetDomainCapsCache(virQEMUCapsPtr qemuCaps);
+
+typedef int (*virQEMUCapsGetDomainCapsCacheFiller)(virDomainCapsPtr domCaps,
+ virQEMUCapsPtr qemuCaps,
+ void *opaque);
+
+virDomainCapsPtr
+virQEMUCapsGetDomainCapsCache(virQEMUCapsPtr qemuCaps,
+ const char *machine,
+ virArch arch,
+ virDomainVirtType virttype,
+ virQEMUCapsGetDomainCapsCacheFiller fillDomainCaps,
+ void *opaque);
+
unsigned int virQEMUCapsGetKVMVersion(virQEMUCapsPtr qemuCaps);
int virQEMUCapsAddCPUDefinitions(virQEMUCapsPtr qemuCaps,
virDomainVirtType type,
diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
index 8040f8ab3a..e0cb8be675 100644
--- a/src/qemu/qemu_conf.c
+++ b/src/qemu/qemu_conf.c
@@ -1337,31 +1337,20 @@ virCapsPtr virQEMUDriverGetCapabilities(virQEMUDriverPtr driver,
}
-struct virQEMUDriverSearchDomcapsData {
- const char *path;
- const char *machine;
- virArch arch;
- virDomainVirtType virttype;
-};
-
-
static int
-virQEMUDriverSearchDomcaps(const void *payload,
- const void *name G_GNUC_UNUSED,
- const void *opaque)
+virQEMUDriverGetDomainCapabilitiesFiller(virDomainCapsPtr domCaps,
+ virQEMUCapsPtr qemuCaps,
+ void *opaque)
{
- virDomainCapsPtr domCaps = (virDomainCapsPtr) payload;
- struct virQEMUDriverSearchDomcapsData *data = (struct virQEMUDriverSearchDomcapsData *) opaque;
-
- if (STREQ_NULLABLE(data->path, domCaps->path) &&
- STREQ_NULLABLE(data->machine, domCaps->machine) &&
- data->arch == domCaps->arch &&
- data->virttype == domCaps->virttype)
- return 1;
+ virQEMUDriverPtr driver = opaque;
+ g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(driver);
- return 0;
+ return virQEMUCapsFillDomainCaps(qemuCaps, driver->hostarch, domCaps,
+ driver->privileged,
+ cfg->firmwares, cfg->nfirmwares);
}
+
/**
* virQEMUDriverGetDomainCapabilities:
*
@@ -1380,40 +1369,12 @@ virQEMUDriverGetDomainCapabilities(virQEMUDriverPtr driver,
virArch arch,
virDomainVirtType virttype)
{
- g_autoptr(virDomainCaps) domCaps = NULL;
- g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(driver);
- virHashTablePtr domCapsCache = virQEMUCapsGetDomainCapsCache(qemuCaps);
- struct virQEMUDriverSearchDomcapsData data = {
- .path = virQEMUCapsGetBinary(qemuCaps),
- .machine = machine,
- .arch = arch,
- .virttype = virttype,
- };
-
- domCaps = virHashSearch(domCapsCache,
- virQEMUDriverSearchDomcaps, &data, NULL);
- if (!domCaps) {
- g_autofree char *key = NULL;
-
- /* hash miss, build new domcaps */
- if (!(domCaps = virDomainCapsNew(data.path, data.machine,
- data.arch, data.virttype)))
- return NULL;
-
- if (virQEMUCapsFillDomainCaps(qemuCaps, driver->hostarch, domCaps,
- driver->privileged,
- cfg->firmwares, cfg->nfirmwares) < 0)
- return NULL;
-
- key = g_strdup_printf("%d:%d:%s:%s", data.arch, data.virttype,
- NULLSTR(data.machine), NULLSTR(data.path));
-
- if (virHashAddEntry(domCapsCache, key, domCaps) < 0)
- return NULL;
- }
-
- virObjectRef(domCaps);
- return g_steal_pointer(&domCaps);
+ return virQEMUCapsGetDomainCapsCache(qemuCaps,
+ machine,
+ arch,
+ virttype,
+ virQEMUDriverGetDomainCapabilitiesFiller,
+ driver);
}
--
2.24.1
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