Fix GFP_KERNEL allocations flags

The kmem_vasprintf(), kmem_vsprintf(), kobj_open_file(), and vn_openat()
functions should all use the kmem_flags_convert() function to generate
the GFP_* flags.  This ensures that they can be safely called in any
context and the correct flags will be used.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #426

module/spl/spl-kmem.c

@@ -80,7 +80,7 @@ kmem_vasprintf(const char *fmt, va_list ap)
 
 	do {
 		va_copy(aq, ap);
-		ptr = kvasprintf(GFP_KERNEL, fmt, aq);
+		ptr = kvasprintf(kmem_flags_convert(KM_SLEEP), fmt, aq);
 		va_end(aq);
 	} while (ptr == NULL);
 
@@ -96,7 +96,7 @@ kmem_asprintf(const char *fmt, ...)
 
 	do {
 		va_start(ap, fmt);
-		ptr = kvasprintf(GFP_KERNEL, fmt, ap);
+		ptr = kvasprintf(kmem_flags_convert(KM_SLEEP), fmt, ap);
 		va_end(ap);
 	} while (ptr == NULL);