Amir Goldstein [off-list ref] writes:

On Fri, Oct 15, 2021 at 12:39 AM Gabriel Krisman Bertazi
[off-list ref] wrote:

quoted

Error events (FAN_FS_ERROR) against the same file system can be merged
by simply iterating the error count.  The hash is taken from the fsid,
without considering the FH.  This means that only the first error object
is reported.

Signed-off-by: Gabriel Krisman Bertazi <redacted>
---
 fs/notify/fanotify/fanotify.c | 39 ++++++++++++++++++++++++++++++++---
 fs/notify/fanotify/fanotify.h |  4 +++-
 2 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 9b970359570a..7032083df62a 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c

@@ -111,6 +111,16 @@ static bool fanotify_name_event_equal(struct fanotify_name_event *fne1,
        return fanotify_info_equal(info1, info2);
 }

+static bool fanotify_error_event_equal(struct fanotify_error_event *fee1,
+                                      struct fanotify_error_event *fee2)
+{
+       /* Error events against the same file system are always merged. */
+       if (!fanotify_fsid_equal(&fee1->fsid, &fee2->fsid))
+               return false;
+
+       return true;
+}
+
 static bool fanotify_should_merge(struct fanotify_event *old,
                                  struct fanotify_event *new)
 {

@@ -141,6 +151,9 @@ static bool fanotify_should_merge(struct fanotify_event *old,
        case FANOTIFY_EVENT_TYPE_FID_NAME:
                return fanotify_name_event_equal(FANOTIFY_NE(old),
                                                 FANOTIFY_NE(new));
+       case FANOTIFY_EVENT_TYPE_FS_ERROR:
+               return fanotify_error_event_equal(FANOTIFY_EE(old),
+                                                 FANOTIFY_EE(new));
        default:
                WARN_ON_ONCE(1);
        }

@@ -148,6 +161,22 @@ static bool fanotify_should_merge(struct fanotify_event *old,
        return false;
 }

+static void fanotify_merge_error_event(struct fanotify_error_event *dest,
+                                      struct fanotify_error_event *origin)
+{
+       dest->err_count++;
+}
+
+static void fanotify_merge_event(struct fanotify_event *dest,
+                                struct fanotify_event *origin)
+{
+       dest->mask |= origin->mask;
+
+       if (origin->type == FANOTIFY_EVENT_TYPE_FS_ERROR)
+               fanotify_merge_error_event(FANOTIFY_EE(dest),
+                                          FANOTIFY_EE(origin));
+}
+
 /* Limit event merges to limit CPU overhead per event */
 #define FANOTIFY_MAX_MERGE_EVENTS 128

@@ -175,7 +204,7 @@ static int fanotify_merge(struct fsnotify_group *group,
                if (++i > FANOTIFY_MAX_MERGE_EVENTS)
                        break;
                if (fanotify_should_merge(old, new)) {
-                       old->mask |= new->mask;
+                       fanotify_merge_event(old, new);
                        return 1;
                }
        }

@@ -577,7 +606,8 @@ static struct fanotify_event *fanotify_alloc_name_event(struct inode *id,
 static struct fanotify_event *fanotify_alloc_error_event(
                                                struct fsnotify_group *group,
                                                __kernel_fsid_t *fsid,
-                                               const void *data, int data_type)
+                                               const void *data, int data_type,
+                                               unsigned int *hash)
 {
        struct fs_error_report *report =
                        fsnotify_data_error_report(data, data_type);

@@ -591,6 +621,9 @@ static struct fanotify_event *fanotify_alloc_error_event(
                return NULL;

        fee->fae.type = FANOTIFY_EVENT_TYPE_FS_ERROR;
+       fee->err_count = 1;
+
+       *hash ^= fanotify_hash_fsid(fsid);

        return &fee->fae;
 }

Forgot to store fee->fsid?

Not really. this is part of the FID info record support, which is done
in patch 23.

-- 
Gabriel Krisman Bertazi