From: SeongJae Park sj@kernel.org
The advertisement of the persistent grants feature (writing 'feature-persistent' to xenbus) should mean not the decision for using the feature but only the availability of the feature. However, commit aac8a70db24b ("xen-blkback: add a parameter for disabling of persistent grants") made a field of blkback, which was a place for saving only the negotiation result, to be used for yet another purpose: caching of the 'feature_persistent' parameter value. As a result, the advertisement, which should follow only the parameter value, becomes inconsistent.
This commit fixes the misuse of the semantic by making blkback saves the parameter value in a separate place and advertises the support based on only the saved value.
Fixes: aac8a70db24b ("xen-blkback: add a parameter for disabling of persistent grants") Cc: stable@vger.kernel.org # 5.10.x Suggested-by: Juergen Gross jgross@suse.com Signed-off-by: SeongJae Park sj@kernel.org Tested-by: Marek Marczykowski-Górecki marmarek@invisiblethingslab.com Reviewed-by: Juergen Gross jgross@suse.com Link: https://lore.kernel.org/r/20220831165824.94815-2-sj@kernel.org Signed-off-by: Juergen Gross jgross@suse.com --- drivers/block/xen-blkback/common.h | 3 +++ drivers/block/xen-blkback/xenbus.c | 6 ++++-- 2 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h index bda5c815e441..a28473470e66 100644 --- a/drivers/block/xen-blkback/common.h +++ b/drivers/block/xen-blkback/common.h @@ -226,6 +226,9 @@ struct xen_vbd { sector_t size; unsigned int flush_support:1; unsigned int discard_secure:1; + /* Connect-time cached feature_persistent parameter value */ + unsigned int feature_gnt_persistent_parm:1; + /* Persistent grants feature negotiation result */ unsigned int feature_gnt_persistent:1; unsigned int overflow_max_grants:1; }; diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index ee7ad2fb432d..c0227dfa4688 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -907,7 +907,7 @@ static void connect(struct backend_info *be) xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);
err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", - be->blkif->vbd.feature_gnt_persistent); + be->blkif->vbd.feature_gnt_persistent_parm); if (err) { xenbus_dev_fatal(dev, err, "writing %s/feature-persistent", dev->nodename); @@ -1085,7 +1085,9 @@ static int connect_ring(struct backend_info *be) return -ENOSYS; }
- blkif->vbd.feature_gnt_persistent = feature_persistent && + blkif->vbd.feature_gnt_persistent_parm = feature_persistent; + blkif->vbd.feature_gnt_persistent = + blkif->vbd.feature_gnt_persistent_parm && xenbus_read_unsigned(dev->otherend, "feature-persistent", 0);
blkif->vbd.overflow_max_grants = 0;