Crash in dbuf_evict_one with DTRACE_PROBE

Update the dbuf__evict__one() tracepoint so that it can safely
handle a NULL dmu_buf_impl_t pointer.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Signed-off-by: gaurkuma <gauravk.18@gmail.com>
Closes #6463

diff --git a/include/sys/trace_dbuf.h b/include/sys/trace_dbuf.h
index edaa77fa68dfc0b19d9d3111c19083fddac47a5d..c3e70c371aa0f899bc1fdbf3a91535e591887c80 100644 (file)
--- a/include/sys/trace_dbuf.h
+++ b/include/sys/trace_dbuf.h
@@ -33,6 +33,10 @@
 #include <linux/tracepoint.h>
 #include <sys/types.h>
 
+#ifndef        TRACE_DBUF_MSG_MAX
+#define        TRACE_DBUF_MSG_MAX      512
+#endif
+
 /*
  * Generic support for two argument tracepoints of the form:
  *
@@ -42,8 +46,7 @@
  */
 
 #define        DBUF_TP_STRUCT_ENTRY                                    \
-       __string(os_spa,                                        \
-           spa_name(DB_DNODE(db)->dn_objset->os_spa))          \
+       __dynamic_array(char,   os_spa, TRACE_DBUF_MSG_MAX)     \
        __field(uint64_t,       ds_object)                      \
        __field(uint64_t,       db_object)                      \
        __field(uint64_t,       db_level)                       \
@@ -52,21 +55,38 @@
        __field(uint64_t,       db_size)                        \
        __field(uint64_t,       db_state)                       \
        __field(int64_t,        db_holds)                       \
-
-#define        DBUF_TP_FAST_ASSIGN                                     \
-       __assign_str(os_spa,                                    \
-           spa_name(DB_DNODE(db)->dn_objset->os_spa));         \
-                                                               \
-       __entry->ds_object = db->db_objset->os_dsl_dataset ?    \
-           db->db_objset->os_dsl_dataset->ds_object : 0;       \
-                                                               \
-       __entry->db_object = db->db.db_object;                  \
-       __entry->db_level  = db->db_level;                      \
-       __entry->db_blkid  = db->db_blkid;                      \
-       __entry->db_offset = db->db.db_offset;                  \
-       __entry->db_size   = db->db.db_size;                    \
-       __entry->db_state  = db->db_state;                      \
-       __entry->db_holds  = refcount_count(&db->db_holds);
+       __dynamic_array(char,   msg,    TRACE_DBUF_MSG_MAX)
+
+#define        DBUF_TP_FAST_ASSIGN                                             \
+       if (db != NULL) {                                               \
+               __assign_str(os_spa,                                    \
+               spa_name(DB_DNODE(db)->dn_objset->os_spa));             \
+                                                                       \
+               __entry->ds_object = db->db_objset->os_dsl_dataset ?    \
+               db->db_objset->os_dsl_dataset->ds_object : 0;           \
+                                                                       \
+               __entry->db_object = db->db.db_object;                  \
+               __entry->db_level  = db->db_level;                      \
+               __entry->db_blkid  = db->db_blkid;                      \
+               __entry->db_offset = db->db.db_offset;                  \
+               __entry->db_size   = db->db.db_size;                    \
+               __entry->db_state  = db->db_state;                      \
+               __entry->db_holds  = refcount_count(&db->db_holds);     \
+               snprintf(__get_str(msg), TRACE_DBUF_MSG_MAX,            \
+                   DBUF_TP_PRINTK_FMT, DBUF_TP_PRINTK_ARGS);           \
+       } else {                                                        \
+               __assign_str(os_spa, "NULL")                            \
+               __entry->ds_object = 0;                                 \
+               __entry->db_object = 0;                                 \
+               __entry->db_level  = 0;                                 \
+               __entry->db_blkid  = 0;                                 \
+               __entry->db_offset = 0;                                 \
+               __entry->db_size   = 0;                                 \
+               __entry->db_state  = 0;                                 \
+               __entry->db_holds  = 0;                                 \
+               snprintf(__get_str(msg), TRACE_DBUF_MSG_MAX,            \
+                   "dbuf { NULL }");                                   \
+       }
 
 #define        DBUF_TP_PRINTK_FMT                                              \
        "dbuf { spa \"%s\" objset %llu object %llu level %llu "         \
@@ -84,7 +104,7 @@ DECLARE_EVENT_CLASS(zfs_dbuf_class,
        TP_ARGS(db, zio),
        TP_STRUCT__entry(DBUF_TP_STRUCT_ENTRY),
        TP_fast_assign(DBUF_TP_FAST_ASSIGN),
-       TP_printk(DBUF_TP_PRINTK_FMT, DBUF_TP_PRINTK_ARGS)
+       TP_printk("%s", __get_str(msg))
 );
 /* END CSTYLED */
 
@@ -102,7 +122,7 @@ DECLARE_EVENT_CLASS(zfs_dbuf_evict_one_class,
        TP_ARGS(db, mls),
        TP_STRUCT__entry(DBUF_TP_STRUCT_ENTRY),
        TP_fast_assign(DBUF_TP_FAST_ASSIGN),
-       TP_printk(DBUF_TP_PRINTK_FMT, DBUF_TP_PRINTK_ARGS)
+       TP_printk("%s", __get_str(msg))
 );
 /* END CSTYLED */