oss-lock-mm-sema.patch

diff --git a/runtime/linux/loc2c-runtime.h b/runtime/linux/loc2c-runtime.h
index 0270fa1a0..718b0fc15 100644
--- a/runtime/linux/loc2c-runtime.h
+++ b/runtime/linux/loc2c-runtime.h
@@ -380,6 +380,15 @@ static inline int __stp_deref_nocheck_(u64 *pv, size_t size, void *addr)
 {
   u64 v = 0;
   int r = -EFAULT;
+  struct mm_struct *mm = current->mm;
+
+  if (mm) {
+    // The down_read() function can sleep, so we'll call
+    // down_read_trylock() instead, which can fail.
+    if (! down_read_trylock(&mm->mmap_sem)) {
+      return -EBUSY;
+    }
+  }
 
   switch (size)
     {
@@ -400,6 +409,9 @@ static inline int __stp_deref_nocheck_(u64 *pv, size_t size, void *addr)
 #endif
     }
 
+  if (mm)
+    up_read(&mm->mmap_sem);
+
   *pv = v;
   return r;
 }
@@ -529,8 +541,12 @@ static inline int _stp_deref_nofault_(u64 *pv, size_t size, void *addr,
       default:								\
 	__stp_get_user_bad();						\
       }									\
-    if (_e)								\
-      DEREF_FAULT(addr);						\
+    if (_e) {								\
+      if (_e == -EBUSY)  						\
+	DEREF_BUSY(addr);						\
+      else								\
+        DEREF_FAULT(addr);						\
+    }									\
     _v;									\
   })
 
@@ -773,6 +789,17 @@ static inline long _stp_deref_string_nofault(char *dst, const char *addr,
     err = 1;
   else
     {
+      struct mm_struct *mm = current->mm;
+      if (mm) {
+        // The down_read() function can sleep, so we'll call
+        // down_read_trylock() instead, which can fail.
+        if (! down_read_trylock(&mm->mmap_sem)) {
+          pagefault_enable();
+          set_fs(oldfs);
+          return -EBUSY;
+        }
+      }
+
       /* Reduce len by 1 to leave room for '\0' terminator. */
       for (i = 0; i + 1 < len; ++i)
 	{
@@ -783,6 +810,10 @@ static inline long _stp_deref_string_nofault(char *dst, const char *addr,
 	  if (dst)
 	    *dst++ = v;
 	}
+
+      if (mm)
+        up_read(&mm->mmap_sem);
+
       if (!err && dst)
 	*dst = '\0';
     }
diff --git a/runtime/loc2c-runtime.h b/runtime/loc2c-runtime.h
index 0502d5a07..7d5f9c7b1 100644
--- a/runtime/loc2c-runtime.h
+++ b/runtime/loc2c-runtime.h
@@ -232,10 +232,19 @@
 
 
 #if STP_SKIP_BADVARS
+#define DEREF_BUSY(addr) ({0; })
 #define DEREF_FAULT(addr) ({0; })
 #define STORE_DEREF_FAULT(addr) ({0; })
 #define CATCH_DEREF_FAULT() ({0; })
 #else
+#define DEREF_BUSY(addr) ({						    \
+    snprintf(c->error_buffer, sizeof(c->error_buffer),			    \
+	     STAP_MSG_LOC2C_00, (int)current->tgid,			    \
+             (long)(intptr_t)(addr));					    \
+    c->last_error = c->error_buffer;					    \
+    goto deref_fault;							    \
+    })
+
 #define DEREF_FAULT(addr) ({						    \
     snprintf(c->error_buffer, sizeof(c->error_buffer),			    \
 	     STAP_MSG_LOC2C_01, (long)(intptr_t)(addr));		    \
diff --git a/tapset/uconversions.stp b/tapset/uconversions.stp
index 83790e992..8654821d2 100644
--- a/tapset/uconversions.stp
+++ b/tapset/uconversions.stp
@@ -124,9 +124,14 @@ function user_string_n:string (addr:long, n:long)
 			(char __user *) (uintptr_t) STAP_ARG_addr, len);
 		if (rc < 0) {
 			strlcpy(STAP_RETVALUE, "<unknown>", MAXSTRINGLEN);
-			snprintf (CONTEXT->error_buffer, sizeof(CONTEXT->error_buffer),
-				"user string copy fault %ld at 0x%lx [man error::fault]", rc,
-				(unsigned long) (uintptr_t) STAP_ARG_addr);
+			if (rc == -EBUSY)
+				snprintf (CONTEXT->error_buffer, sizeof(CONTEXT->error_buffer),
+					"mm sem busy in user string copy %ld at 0x%lx [man error::fault]", rc,
+					(uintptr_t) STAP_ARG_addr);
+			else
+				snprintf (CONTEXT->error_buffer, sizeof(CONTEXT->error_buffer),
+					"user string copy fault %ld at 0x%lx [man error::fault]", rc,
+					(uintptr_t) STAP_ARG_addr);
 			CONTEXT->last_error = CONTEXT->error_buffer;
 		} else
 			STAP_RETVALUE[len - 1] = '\0';
diff --git a/translate.cxx b/translate.cxx
index a29d9da29..b504066b9 100644
--- a/translate.cxx
+++ b/translate.cxx
@@ -7862,6 +7862,8 @@ void translate_runtime(systemtap_session& s)
                   << lex_cast_qstring(_("myproc-unprivileged tapset function called "
                                         "without is_myproc checking for pid %d (euid %d)"));
 
+  s.op->newline() << "#define STAP_MSG_LOC2C_00 "
+                  << lex_cast_qstring(_("pid %d: mm sem busy [man error::fault] at 0x%lx"));
   s.op->newline() << "#define STAP_MSG_LOC2C_01 "
                   << lex_cast_qstring(_("read fault [man error::fault] at 0x%lx"));
   s.op->newline() << "#define STAP_MSG_LOC2C_02 "