From: Lucian Petrut <lpetrut@cloudbasesolutions.com>
Date: Thu, 27 Apr 2023 12:44:51 +0000 (+0000)
Subject: librbd: avoid decrementing iterator before first element
X-Git-Tag: v18.1.2~46^2
X-Git-Url: http://git.apps.os.sepia.ceph.com/?a=commitdiff_plain;h=fabca81423b5270f3143baa636079b5c40edfba2;p=ceph-ci.git

librbd: avoid decrementing iterator before first element

While trying to merge delayed requests, SimpleSchedulerObjectDispatch
can end up iterating before the first element.

With llvm, this leads to a crash:
https://paste.opendev.org/raw/bxnQqqDtIrkOfVvRfkZ6/

This change adds a check, ensuring that we won't decrement the iterator
before the first map element.

Fixes: https://tracker.ceph.com/issues/61503
Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>
(cherry picked from commit ca65e85575f7b35ce679309e92e0c9bee8d6b96a)
---

diff --git a/src/librbd/io/SimpleSchedulerObjectDispatch.cc b/src/librbd/io/SimpleSchedulerObjectDispatch.cc
index 6b50c46ad52..cd2ffb1975d 100644
--- a/src/librbd/io/SimpleSchedulerObjectDispatch.cc
+++ b/src/librbd/io/SimpleSchedulerObjectDispatch.cc
@@ -105,7 +105,8 @@ bool SimpleSchedulerObjectDispatch<I>::ObjectRequests::try_delay_request(
 
     // try to merge back to an existing request
     iter = m_delayed_requests.lower_bound(object_off);
-    if (iter == m_delayed_requests.end() || iter->first > object_off) {
+    if (iter != m_delayed_requests.begin() &&
+        (iter == m_delayed_requests.end() || iter->first > object_off)) {
       iter--;
     }
     if (iter != m_delayed_requests.end() &&