sfc: Fix loop condition for efx_filter_search() when !for_insert

efx_filter_remove_filter() fails to remove inserted filters in some cases.

For example:

  1. Two filters A and B have specifications that result in an initial
     hash collision.
  2. A is inserted first, followed by B.
  3. An attempt to remove B first succeeds, but if A is removed first
     a subsequent attempt to remove B fails.

When searching for an existing filter (!for_insert),
efx_filter_search() must always continue to the maximum search depth
for the given type rather than stopping at the first unused entry.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

1 files changed, 24 insertions, 17 deletions

diff --git a/drivers/net/sfc/filter.c b/drivers/net/sfc/filter.c
index f2fc2587c09..054f0a3d45a 100644
--- a/drivers/net/sfc/filter.c
+++ b/drivers/net/sfc/filter.c
@@ -335,28 +335,35 @@ static int efx_filter_search(struct efx_filter_table *table,
                              bool for_insert, int *depth_required)
 {
         unsigned hash, incr, filter_idx, depth, depth_max;
-        struct efx_filter_spec *cmp;
 
         hash = efx_filter_hash(key);
         incr = efx_filter_increment(key);
-        depth_max = (spec->priority <= EFX_FILTER_PRI_HINT ?
-                     FILTER_CTL_SRCH_HINT_MAX : FILTER_CTL_SRCH_MAX);
-
-        for (depth = 1, filter_idx = hash & (table->size - 1);
-             depth <= depth_max && test_bit(filter_idx, table->used_bitmap);
-             ++depth) {
-                cmp = &table->spec[filter_idx];
-                if (efx_filter_equal(spec, cmp))
-                        goto found;
+
+        filter_idx = hash & (table->size - 1);
+        depth = 1;
+        depth_max = (for_insert ?
+                     (spec->priority <= EFX_FILTER_PRI_HINT ?
+                      FILTER_CTL_SRCH_HINT_MAX : FILTER_CTL_SRCH_MAX) :
+                     table->search_depth[spec->type]);
+
+        for (;;) {
+                /* Return success if entry is used and matches this spec
+                 * or entry is unused and we are trying to insert.
+                 */
+                if (test_bit(filter_idx, table->used_bitmap) ?
+                    efx_filter_equal(spec, &table->spec[filter_idx]) :
+                    for_insert) {
+                        *depth_required = depth;
+                        return filter_idx;
+                }
+
+                /* Return failure if we reached the maximum search depth */
+                if (depth == depth_max)
+                        return for_insert ? -EBUSY : -ENOENT;
+
                 filter_idx = (filter_idx + incr) & (table->size - 1);
+                ++depth;
         }
-        if (!for_insert)
-                return -ENOENT;
-        if (depth > depth_max)
-                return -EBUSY;
-found:
-        *depth_required = depth;
-        return filter_idx;
 }
 
 /* Construct/deconstruct external filter IDs */