[PATCH] virObject: Error on suspicious ref and unref

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



https://bugzilla.redhat.com/show_bug.cgi?id=1033061

Since our transformation into virObject is not complete and we must do
ref and unref ourselves there's a chance that we will get it wrong. That
is, while one thread is doing unref and subsequent dispose another
thread may come and do the ref & unref on stale pointer. This results in
dispose being called twice (and possibly simultaneously). These kind of
errors are hard to catch so we should at least throw an error into logs
if such situation occurs. In fact, I've seen a stack trace showing this
error had happen (obj = 0x7f4968018260):

Thread 2 (Thread 0x7f498596b880 (LWP 13394)):
[...]
 #4  0x00007f496ff44607 in ncf_close (ncf=0x7f496801e3d0) at netcf.c:101
        __PRETTY_FUNCTION__ = "ncf_close"
 #5  0x00007f4984f3f31b in virObjectUnref (anyobj=<optimized out>) at util/virobject.c:262
        klass = 0x7f4968019020
        obj = 0x7f4968018260
        lastRef = true
        __func__ = "virObjectUnref"
 #6  0x00007f4970159785 in netcfStateCleanup () at interface/interface_backend_netcf.c:109
 No locals.
 #7  0x00007f4984fc0e28 in virStateCleanup () at libvirt.c:883
        i = 6
        ret = 0
 #8  0x00007f49859b55fd in main (argc=<optimized out>, argv=<optimized out>) at libvirtd.c:1549
        srv = 0x7f498696ed00
        remote_config_file = 0x0
        statuswrite = -1
        ret = <optimized out>
        pid_file_fd = 5
        pid_file = 0x0
        sock_file = 0x0
        sock_file_ro = 0x0
        timeout = -1
        verbose = 0
        godaemon = 0
        ipsock = 0
        config = 0x7f498696e760
        privileged = <optimized out>
        implicit_conf = <optimized out>
        run_dir = 0x0
        old_umask = <optimized out>
        opts = {{name = 0x7f49859e2b53 "verbose", has_arg = 0, flag = 0x7fff45057808, val = 118}, {name = 0x7f49859e2b5b "daemon", has_arg = 0, flag = 0x7fff4505780c, val = 100}, {name = 0x7f49859e2b62 "listen", has_arg = 0, flag = 0x7fff45057810, val = 108}, {name = 0x7f49859e2c9f "config", has_arg = 1, flag = 0x0, val = 102}, {name = 0x7f49859e2c00 "timeout", has_arg = 1, flag = 0x0, val = 116}, {name = 0x7f49859e2b69 "pid-file", has_arg = 1, flag = 0x0, val = 112}, {name = 0x7f49859e2b72 "version", has_arg = 0, flag = 0x0, val = 86}, {name = 0x7f49859e2b7a "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x0, has_arg = 0, flag = 0x0, val = 0}}
        __func__ = "main"

Thread 1 (Thread 0x7f496d6a4700 (LWP 13405)):
[...]
 #6  0x00007f496ff44607 in ncf_close (ncf=0x7f496801e3d0) at netcf.c:101
        __PRETTY_FUNCTION__ = "ncf_close"
 #7  0x00007f4984f3f31b in virObjectUnref (anyobj=<optimized out>) at util/virobject.c:262
        klass = 0x7f4968019020
        obj = 0x7f4968018260
        lastRef = true
        __func__ = "virObjectUnref"
 #8  0x00007f4970157752 in netcfInterfaceClose (conn=0x7f49680a3260) at interface/interface_backend_netcf.c:265
 No locals.
 #9  0x00007f4984fb7984 in virConnectDispose (obj=0x7f49680a3260) at datatypes.c:149
        conn = 0x7f49680a3260
 #10 0x00007f4984f3f31b in virObjectUnref (anyobj=anyobj@entry=0x7f49680a3260) at util/virobject.c:262
        klass = 0x7f49681d6760
        obj = 0x7f49680a3260
        lastRef = true
        __func__ = "virObjectUnref"
 #11 0x00007f4984fc11bf in virConnectClose (conn=conn@entry=0x7f49680a3260) at libvirt.c:1532
        __func__ = "virConnectClose"
        __FUNCTION__ = "virConnectClose"
 #12 0x00007f496eced281 in virLXCProcessAutostartAll (driver=0x7f49681ffaa0) at lxc/lxc_process.c:1426
        conn = 0x7f49680a3260
        data = {driver = 0x7f49681ffaa0, conn = 0x7f49680a3260}
 #13 0x00007f4984fc0d21 in virStateInitialize (privileged=true, callback=callback@entry=0x7f49859b7180 <daemonInhibitCallback>, opaque=opaque@entry=0x7f498696ed00) at libvirt.c:864
        i = 8
        __func__ = "virStateInitialize"
 #14 0x00007f49859b71db in daemonRunStateInit (opaque=opaque@entry=0x7f498696ed00) at libvirtd.c:906
        srv = 0x7f498696ed00
        sysident = 0x7f4968000ae0
        __func__ = "daemonRunStateInit"
 #15 0x00007f4984f4efe1 in virThreadHelper (data=<optimized out>) at util/virthreadpthread.c:161
        args = 0x0
        local = {func = 0x7f49859b71a0 <daemonRunStateInit>, opaque = 0x7f498696ed00}
 #16 0x00007f4982a40de3 in start_thread (arg=0x7f496d6a4700) at pthread_create.c:308
        __res = <optimized out>
        pd = 0x7f496d6a4700
        now = <optimized out>
        unwind_buf = {cancel_jmp_buf = {{jmp_buf = {139953345021696, 7118305506502180663, 0, 139953345022400, 139953345021696, 140734351374104, -7179978120810397897, -7180347023594422473}, mask_was_saved = 0}}, priv = {pad = {0x0, 0x0, 0x0, 0x0}, data = {prev = 0x0, cleanup = 0x0, canceltype = 0}}}
        not_first_call = <optimized out>
        pagesize_m1 = <optimized out>
        sp = <optimized out>
        freesize = <optimized out>
 #17 0x00007f498236716d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:113

Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
---
 src/nwfilter/nwfilter_dhcpsnoop.c |  6 ++---
 src/util/viratomic.h              | 53 +++++++++++++++++++++++++++++++--------
 src/util/virobject.c              | 17 ++++++++++---
 3 files changed, 58 insertions(+), 18 deletions(-)

diff --git a/src/nwfilter/nwfilter_dhcpsnoop.c b/src/nwfilter/nwfilter_dhcpsnoop.c
index e8fcfef..71380bb 100644
--- a/src/nwfilter/nwfilter_dhcpsnoop.c
+++ b/src/nwfilter/nwfilter_dhcpsnoop.c
@@ -893,7 +893,7 @@ virNWFilterSnoopReqLeaseDel(virNWFilterSnoopReqPtr req,
 skip_instantiate:
     VIR_FREE(ipl);
 
-    virAtomicIntDecAndTest(&virNWFilterSnoopState.nLeases);
+    virAtomicIntDec(&virNWFilterSnoopState.nLeases);
 
 lease_not_found:
     VIR_FREE(ipstr);
@@ -1169,7 +1169,7 @@ static void virNWFilterDHCPDecodeWorker(void *jobdata, void *opaque)
                        _("Instantiation of rules failed on "
                          "interface '%s'"), req->ifname);
     }
-    virAtomicIntDecAndTest(job->qCtr);
+    virAtomicIntDec(job->qCtr);
     VIR_FREE(job);
 }
 
@@ -1562,7 +1562,7 @@ exit:
             pcap_close(pcapConf[i].handle);
     }
 
-    virAtomicIntDecAndTest(&virNWFilterSnoopState.nThreads);
+    virAtomicIntDec(&virNWFilterSnoopState.nThreads);
 
     return;
 }
diff --git a/src/util/viratomic.h b/src/util/viratomic.h
index 4d7f7e5..877900e 100644
--- a/src/util/viratomic.h
+++ b/src/util/viratomic.h
@@ -68,6 +68,18 @@ VIR_STATIC int virAtomicIntInc(volatile int *atomic)
     ATTRIBUTE_NONNULL(1);
 
 /**
+ * virAtomicIntDec:
+ * Decrements the value of atomic by 1.
+ *
+ * Think of this operation as an atomic version of
+ * { *atomic -= 1; return *atomic == 0; }
+ *
+ * This call acts as a full compiler and hardware memory barrier.
+ */
+VIR_STATIC int virAtomicIntDec(volatile int *atomic)
+    ATTRIBUTE_NONNULL(1);
+
+/**
  * virAtomicIntDecAndTest:
  * Decrements the value of atomic by 1.
  *
@@ -75,6 +87,8 @@ VIR_STATIC int virAtomicIntInc(volatile int *atomic)
  * { *atomic -= 1; return *atomic == 0; }
  *
  * This call acts as a full compiler and hardware memory barrier.
+ * Returns true if the resulting decremented value is zero,
+ * false otherwise.
  */
 VIR_STATIC bool virAtomicIntDecAndTest(volatile int *atomic)
     ATTRIBUTE_NONNULL(1);
@@ -176,12 +190,15 @@ VIR_STATIC unsigned int virAtomicIntXor(volatile unsigned int *atomic,
             (void)(0 ? *(atomic) ^ *(atomic) : 0);                      \
             __sync_add_and_fetch((atomic), 1);                          \
         }))
+#  define virAtomicIntDec(atomic)                                       \
+    (__extension__ ({                                                   \
+            (void)verify_true(sizeof(*(atomic)) == sizeof(int));        \
+            (void)(0 ? *(atomic) ^ *(atomic) : 0);                      \
+            __sync_sub_and_fetch((atomic), 1);                          \
+        }))
 #  define virAtomicIntDecAndTest(atomic)                                \
-    (__extension__ ({                                                   \
-            (void)verify_true(sizeof(*(atomic)) == sizeof(int));        \
-            (void)(0 ? *(atomic) ^ *(atomic) : 0);                      \
-            __sync_fetch_and_sub((atomic), 1) == 1;                     \
-        }))
+        (virAtomicIntDec(atomic) == 0)
+
 #  define virAtomicIntCompareExchange(atomic, oldval, newval)           \
     (__extension__ ({                                                   \
             (void)verify_true(sizeof(*(atomic)) == sizeof(int));        \
@@ -252,10 +269,16 @@ virAtomicIntInc(volatile int *atomic)
     return InterlockedIncrement((volatile LONG *)atomic);
 }
 
+static inline int
+virAtomicIntDec(volatile int *atomic)
+{
+    return InterlockedDecrement((volatile LONG *)atomic);
+}
+
 static inline bool
 virAtomicIntDecAndTest(volatile int *atomic)
 {
-    return InterlockedDecrement((volatile LONG *)atomic) == 0;
+    return virAtomicIntDec(atomic) == 0;
 }
 
 static inline bool
@@ -334,16 +357,22 @@ virAtomicIntInc(volatile int *atomic)
     return value;
 }
 
-static inline bool
-virAtomicIntDecAndTest(volatile int *atomic)
+static inline int
+virAtomicIntDec(volatile int *atomic)
 {
-    bool is_zero;
+    bool value;
 
     pthread_mutex_lock(&virAtomicLock);
-    is_zero = --(*atomic) == 0;
+    value = --(*atomic);
     pthread_mutex_unlock(&virAtomicLock);
 
-    return is_zero;
+    return value;
+}
+
+static inline int
+virAtomicIntDecAndTest(volatile int *atomic)
+{
+    return virAtomicIntDec(atomic) == 0;
 }
 
 static inline bool
@@ -436,6 +465,8 @@ virAtomicIntXor(volatile unsigned int *atomic,
     virAtomicIntSet((int *)atomic, val)
 #  define virAtomicIntInc(atomic)               \
     virAtomicIntInc((int *)atomic)
+#  define virAtomicIntDec(atomic)               \
+    virAtomicIntDec((int *)atomic)
 #  define virAtomicIntDecAndTest(atomic)        \
     virAtomicIntDecAndTest((int *)atomic)
 #  define virAtomicIntCompareExchange(atomic, oldval, newval)   \
diff --git a/src/util/virobject.c b/src/util/virobject.c
index 61b5413..4299432 100644
--- a/src/util/virobject.c
+++ b/src/util/virobject.c
@@ -252,9 +252,9 @@ bool virObjectUnref(void *anyobj)
     if (!obj)
         return false;
 
-    bool lastRef = virAtomicIntDecAndTest(&obj->refs);
+    int newRefs = virAtomicIntDec(&obj->refs);
     PROBE(OBJECT_UNREF, "obj=%p", obj);
-    if (lastRef) {
+    if (newRefs == 0) {
         PROBE(OBJECT_DISPOSE, "obj=%p", obj);
         virClassPtr klass = obj->klass;
         while (klass) {
@@ -268,9 +268,13 @@ bool virObjectUnref(void *anyobj)
         obj->magic = 0xDEADBEEF;
         obj->klass = (void*)0xDEADBEEF;
         VIR_FREE(obj);
+    } else if (newRefs < 0) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("Suspicious unrefing of object %p"),
+                       anyobj);
     }
 
-    return !lastRef;
+    return newRefs > 0;
 }
 
 
@@ -289,8 +293,13 @@ void *virObjectRef(void *anyobj)
 
     if (!obj)
         return NULL;
-    virAtomicIntInc(&obj->refs);
+    bool firstRef = virAtomicIntInc(&obj->refs) <= 1;
     PROBE(OBJECT_REF, "obj=%p", obj);
+    if (firstRef) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("Suspicious refing of object %p"),
+                       anyobj);
+    }
     return anyobj;
 }
 
-- 
1.8.4.4

--
libvir-list mailing list
libvir-list@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/libvir-list




[Index of Archives]     [Virt Tools]     [Libvirt Users]     [Lib OS Info]     [Fedora Users]     [Fedora Desktop]     [Fedora SELinux]     [Big List of Linux Books]     [Yosemite News]     [KDE Users]     [Fedora Tools]