From ae05de3e9b2e9868216e5168e50dfcb5074684cb Mon Sep 17 00:00:00 2001
From: xie xingguo <xie.xingguo@zte.com.cn>
Date: Tue, 16 Jun 2020 10:08:32 +0800
Subject: [PATCH] common, osd: add sanity checks around
 osd_scrub_max_preemptions
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to limit maximum preempt_divisor we can use when backing off the
chunky-scrub range on preempting.

Otherwise large osd_scrub_max_preemptions values (i.e., >= 32)
would cause preempt_divisor overflow, hence the dreaded
“divide by zero error”.

Fixes: https://tracker.ceph.com/issues/46024
Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>
---
 src/common/options.cc | 1 +
 src/osd/PG.cc         | 1 +
 2 files changed, 2 insertions(+)

diff --git a/src/common/options.cc b/src/common/options.cc
index 495dc5273c136..6e0430375ed8e 100644
--- a/src/common/options.cc
+++ b/src/common/options.cc
@@ -3257,6 +3257,7 @@ std::vector<Option> get_global_options() {
 
     Option("osd_scrub_max_preemptions", Option::TYPE_UINT, Option::LEVEL_ADVANCED)
     .set_default(5)
+    .set_min_max(0, 30)
     .set_description("Set the maximum number of times we will preempt a deep scrub due to a client operation before blocking client IO to complete the scrub"),
 
     Option("osd_deep_scrub_interval", Option::TYPE_FLOAT, Option::LEVEL_ADVANCED)
diff --git a/src/osd/PG.cc b/src/osd/PG.cc
index cd3081d202ea4..607833ee15f8f 100644
--- a/src/osd/PG.cc
+++ b/src/osd/PG.cc
@@ -2730,6 +2730,7 @@ void PG::chunky_scrub(ThreadPool::TPHandle &handle)
 	   * left end of the range if we are a tier because they may legitimately
 	   * not exist (see _scrub).
 	   */
+          ceph_assert(scrubber.preempt_divisor > 0);
 	  int min = std::max<int64_t>(3, cct->_conf->osd_scrub_chunk_min /
 				      scrubber.preempt_divisor);
 	  int max = std::max<int64_t>(min, cct->_conf->osd_scrub_chunk_max /
-- 
2.39.5