LU-8808 mdt: avoid out of order ChangeLog during restore

In hsm_cdt_request_completed(), upon restore completion, layout
lock is returned before associated ChangeLog entry has been created.
This allows for a timing window where concurrent file updater can
take control and create its own ChangeLog out of order (before
restore ChangeLog).
This can puzzle, ChangeLog readers (like RobinHood), and have them
think of a wrong file state.
This patch fixes this hole by posting restore ChangeLog before
giving back layout lock.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I958cb61aab34a6a0edc97f4d1390eed623631c21
Reviewed-on: https://review.whamcloud.com/23638
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Henri Doreau <henri.doreau@cea.fr>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>

diff --git a/lustre/mdt/mdt_coordinator.c b/lustre/mdt/mdt_coordinator.c
index a981809..da11033 100644 (file)
--- a/lustre/mdt/mdt_coordinator.c
+++ b/lustre/mdt/mdt_coordinator.c
@@ -1141,12 +1141,13 @@ static int hsm_cdt_request_completed(struct mdt_thread_info *mti,
        int                      cl_flags = 0, rc = 0;
        struct md_hsm            mh;
        bool                     is_mh_changed;
+       bool                     need_changelog = true;
        ENTRY;
 
        /* default is to retry */
        *status = ARS_WAITING;
 
-       /* find object by FID
+       /* find object by FID, mdt_hsm_get_md_hsm() returns obj or err
         * if error/removed continue anyway to get correct reporting done */
        obj = mdt_hsm_get_md_hsm(mti, &car->car_hai->hai_fid, &mh);
        /* we will update MD HSM only if needed */
@@ -1305,6 +1306,13 @@ static int hsm_cdt_request_completed(struct mdt_thread_info *mti,
                if (*status == ARS_WAITING)
                        GOTO(out, rc);
 
+               /* restore special case, need to create ChangeLog record
+                * before to give back layout lock to avoid concurrent
+                * file updater to post out of order ChangeLog */
+               mo_changelog(env, CL_HSM, cl_flags, mdt->mdt_child,
+                            &car->car_hai->hai_fid);
+               need_changelog = false;
+
                /* give back layout lock */
                mutex_lock(&cdt->cdt_restore_lock);
                crh = mdt_hsm_restore_hdl_find(cdt, &car->car_hai->hai_fid);
@@ -1326,8 +1334,9 @@ static int hsm_cdt_request_completed(struct mdt_thread_info *mti,
 
 out:
        /* always add a ChangeLog record */
-       mo_changelog(env, CL_HSM, cl_flags, mdt->mdt_child,
-                    &car->car_hai->hai_fid);
+       if (need_changelog)
+               mo_changelog(env, CL_HSM, cl_flags, mdt->mdt_child,
+                            &car->car_hai->hai_fid);
 
        if (!IS_ERR(obj))
                mdt_object_put(mti->mti_env, obj);