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[PATCH 3/3] tools/oxenstored: mkdir conflicts were sometimes missed

  • To: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Wed, 3 Feb 2021 17:35:49 +0000
  • Authentication-results: esa2.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none
  • Cc: Edwin Török <edvin.torok@xxxxxxxxxx>, "Christian Lindig" <christian.lindig@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, "Wei Liu" <wl@xxxxxxx>
  • Delivery-date: Wed, 03 Feb 2021 17:36:14 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

From: Edwin Török <edvin.torok@xxxxxxxxxx>

Due to how set_write_lowpath was used here it didn't detect create/delete
conflicts.  When we create an entry we must mark our parent as modified
(this is what creating a new node via write does).

Otherwise we can have 2 transactions one creating, and another deleting a node
both succeeding depending on timing.  Or one transaction reading an entry,
concluding it doesn't exist, do some other work based on that information and
successfully commit even if another transaction creates the node via mkdir

Signed-off-by: Edwin Török <edvin.torok@xxxxxxxxxx>
CC: Christian Lindig <christian.lindig@xxxxxxxxxx>
CC: Ian Jackson <iwj@xxxxxxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
 tools/ocaml/xenstored/transaction.ml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/ocaml/xenstored/transaction.ml 
index 25bc8c3b4a..17b1bdf2ea 100644
--- a/tools/ocaml/xenstored/transaction.ml
+++ b/tools/ocaml/xenstored/transaction.ml
@@ -165,7 +165,7 @@ let write t perm path value =
 let mkdir ?(with_watch=true) t perm path =
        Store.mkdir t.store perm path;
-       set_write_lowpath t path;
+       set_write_lowpath t (Store.Path.get_parent path);
        if with_watch then
                add_wop t Xenbus.Xb.Op.Mkdir path



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