drm/i915: Break up the large vsnprintf() in print_error_buffers()

So it appears that I have encountered some bogosity when trying to call
i915_error_printf() with many arguments from print_error_buffers(). The
symptom is that the vsnprintf parser tries to interpret an integer arg
as a character string, the resulting OOPS indicating stack corruption.
Replacing the single call with its 13 format specifiers and arguments
with multiple calls to i915_error_printf() worked fine. This patch goes
one step further and introduced i915_error_puts() to pass the strings
simply.

It may not fix the root cause, but it does prevent my box from dying and
I think helps make print_error_buffers() more friendly.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=66077
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 79 insertions, 30 deletions

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 04cf6c09710a..47d6c748057e 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -647,41 +647,44 @@ static const char *purgeable_flag(int purgeable)
         return purgeable ? " purgeable" : "";
 }
 
-static void i915_error_vprintf(struct drm_i915_error_state_buf *e,
-                               const char *f, va_list args)
+static bool __i915_error_ok(struct drm_i915_error_state_buf *e)
 {
-        unsigned len;
 
         if (!e->err && WARN(e->bytes > (e->size - 1), "overflow")) {
                 e->err = -ENOSPC;
-                return;
+                return false;
         }
 
         if (e->bytes == e->size - 1 || e->err)
-                return;
+                return false;
 
-        /* Seek the first printf which is hits start position */
-        if (e->pos < e->start) {
-                len = vsnprintf(NULL, 0, f, args);
-                if (e->pos + len <= e->start) {
-                        e->pos += len;
-                        return;
-                }
+        return true;
+}
 
-                /* First vsnprintf needs to fit in full for memmove*/
-                if (len >= e->size) {
-                        e->err = -EIO;
-                        return;
-                }
+static bool __i915_error_seek(struct drm_i915_error_state_buf *e,
+                              unsigned len)
+{
+        if (e->pos + len <= e->start) {
+                e->pos += len;
+                return false;
         }
 
-        len = vsnprintf(e->buf + e->bytes, e->size - e->bytes, f, args);
-        if (len >= e->size - e->bytes)
-                len = e->size - e->bytes - 1;
+        /* First vsnprintf needs to fit in its entirety for memmove */
+        if (len >= e->size) {
+                e->err = -EIO;
+                return false;
+        }
 
+        return true;
+}
+
+static void __i915_error_advance(struct drm_i915_error_state_buf *e,
+                                 unsigned len)
+{
         /* If this is first printf in this window, adjust it so that
          * start position matches start of the buffer
          */
+
         if (e->pos < e->start) {
                 const size_t off = e->start - e->pos;
 
@@ -701,6 +704,51 @@ static void i915_error_vprintf(struct drm_i915_error_state_buf *e,
         e->pos += len;
 }
 
+static void i915_error_vprintf(struct drm_i915_error_state_buf *e,
+                               const char *f, va_list args)
+{
+        unsigned len;
+
+        if (!__i915_error_ok(e))
+                return;
+
+        /* Seek the first printf which is hits start position */
+        if (e->pos < e->start) {
+                len = vsnprintf(NULL, 0, f, args);
+                if (!__i915_error_seek(e, len))
+                        return;
+        }
+
+        len = vsnprintf(e->buf + e->bytes, e->size - e->bytes, f, args);
+        if (len >= e->size - e->bytes)
+                len = e->size - e->bytes - 1;
+
+        __i915_error_advance(e, len);
+}
+
+static void i915_error_puts(struct drm_i915_error_state_buf *e,
+                            const char *str)
+{
+        unsigned len;
+
+        if (!__i915_error_ok(e))
+                return;
+
+        len = strlen(str);
+
+        /* Seek the first printf which is hits start position */
+        if (e->pos < e->start) {
+                if (!__i915_error_seek(e, len))
+                        return;
+        }
+
+        if (len >= e->size - e->bytes)
+                len = e->size - e->bytes - 1;
+        memcpy(e->buf + e->bytes, str, len);
+
+        __i915_error_advance(e, len);
+}
+
 void i915_error_printf(struct drm_i915_error_state_buf *e, const char *f, ...)
 {
         va_list args;
@@ -711,6 +759,7 @@ void i915_error_printf(struct drm_i915_error_state_buf *e, const char *f, ...)
 }
 
 #define err_printf(e, ...) i915_error_printf(e, __VA_ARGS__)
+#define err_puts(e, s) i915_error_puts(e, s)
 
 static void print_error_buffers(struct drm_i915_error_state_buf *m,
                                 const char *name,
@@ -720,26 +769,26 @@ static void print_error_buffers(struct drm_i915_error_state_buf *m,
         err_printf(m, "%s [%d]:\n", name, count);
 
         while (count--) {
-                err_printf(m, "  %08x %8u %02x %02x %x %x%s%s%s%s%s%s%s",
+                err_printf(m, "  %08x %8u %02x %02x %x %x",
                            err->gtt_offset,
                            err->size,
                            err->read_domains,
                            err->write_domain,
-                           err->rseqno, err->wseqno,
-                           pin_flag(err->pinned),
-                           tiling_flag(err->tiling),
-                           dirty_flag(err->dirty),
-                           purgeable_flag(err->purgeable),
-                           err->ring != -1 ? " " : "",
-                           ring_str(err->ring),
-                           cache_level_str(err->cache_level));
+                           err->rseqno, err->wseqno);
+                err_puts(m, pin_flag(err->pinned));
+                err_puts(m, tiling_flag(err->tiling));
+                err_puts(m, dirty_flag(err->dirty));
+                err_puts(m, purgeable_flag(err->purgeable));
+                err_puts(m, err->ring != -1 ? " " : "");
+                err_puts(m, ring_str(err->ring));
+                err_puts(m, cache_level_str(err->cache_level));
 
                 if (err->name)
                         err_printf(m, " (name: %d)", err->name);
                 if (err->fence_reg != I915_FENCE_REG_NONE)
                         err_printf(m, " (fence: %d)", err->fence_reg);
 
-                err_printf(m, "\n");
+                err_puts(m, "\n");
                 err++;
         }
 }