[xen staging] tools/xenstored: liveupdate: Properly check long transaction

[patchbot@xxxxxxx]

commit 5d16679ab0760dbe5e4df52c02f15c69ed5541e6
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Wed Mar 3 17:05:26 2021 +0000
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Thu Mar 4 15:36:24 2021 +0000

    tools/xenstored: liveupdate: Properly check long transaction
    
    As XenStored is single-threaded, conn->ta_start_time will always be
    smaller than now. As we substract the latter from the former, it means
    a transaction will never be considered long running.
    
    Invert the two operands of the substraction in both lu_reject_reason()
    and lu_check_allowed(). In addition to that, the former also needs to
    check that conn->ta_start_time is not 0 (i.e the transaction is not
    active).
    
    Take the opportunity to document the return condition of
    lu_check_allowed().
    
    Fixes: e04e53a5be20 ("tools/xenstore: allow live update only with no 
transaction active")
    Reported-by: Bjoern Doebel <doebel@xxxxxxxxx>
    Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
---
 tools/xenstore/xenstored_control.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/tools/xenstore/xenstored_control.c 
b/tools/xenstore/xenstored_control.c
index 766b243839..a1652219b2 100644
--- a/tools/xenstore/xenstored_control.c
+++ b/tools/xenstore/xenstored_control.c
@@ -459,11 +459,18 @@ static bool lu_check_lu_allowed(void)
        list_for_each_entry(conn, &connections, list) {
                if (conn->ta_start_time) {
                        ta_total++;
-                       if (conn->ta_start_time - now >= lu_status->timeout)
+                       if (now - conn->ta_start_time >= lu_status->timeout)
                                ta_long++;
                }
        }
 
+       /*
+        * Allow LiveUpdate if one of the following conditions is met:
+        *      - There is no active transactions
+        *      - All transactions are long running (e.g. they have been
+        *      active for more than lu_status->timeout sec) and the admin as
+        *      requested to force the operation.
+        */
        return ta_total ? (lu_status->force && ta_long == ta_total) : true;
 }
 
@@ -474,11 +481,12 @@ static const char *lu_reject_reason(const void *ctx)
        time_t now = time(NULL);
 
        list_for_each_entry(conn, &connections, list) {
-               if (conn->ta_start_time - now >= lu_status->timeout) {
+               if (conn->ta_start_time &&
+                   (now - conn->ta_start_time >= lu_status->timeout)) {
                        ret = talloc_asprintf(ctx, "%s\nDomain %u: %ld s",
                                              ret ? : "Domains with long 
running transactions:",
                                              conn->id,
-                                             conn->ta_start_time - now);
+                                             now - conn->ta_start_time);
                }
        }
 
--
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