From fc29fd83894d0d72f1384b880dd2fdc31af98df5 Mon Sep 17 00:00:00 2001
From: guybe7 <guy.benoish@redislabs.com>
Date: Tue, 13 Oct 2020 18:50:57 +0200
Subject: [PATCH] performEvictions: mem_freed may be negative (#7908)

If 'delta' is negative 'mem_freed' may underflow and cause
the while loop to exit prematurely (And not evicting enough
memory)

mem_freed can be negative when:
1. We use lazy free (consuming memory by appending to a list)
2. Thread doing an allocation between the two calls to zmalloc_used_memory.
---
 src/evict.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/evict.c b/src/evict.c
index 0e8f818ff..d14603aef 100644
--- a/src/evict.c
+++ b/src/evict.c
@@ -499,7 +499,8 @@ int performEvictions(void) {
     if (!isSafeToPerformEvictions()) return EVICT_OK;
 
     int keys_freed = 0;
-    size_t mem_reported, mem_tofree, mem_freed;
+    size_t mem_reported, mem_tofree;
+    long long mem_freed; /* May be negative */
     mstime_t latency, eviction_latency;
     long long delta;
     int slaves = listLength(server.slaves);
@@ -520,7 +521,7 @@ int performEvictions(void) {
     monotime evictionTimer;
     elapsedStart(&evictionTimer);
 
-    while (mem_freed < mem_tofree) {
+    while (mem_freed < (long long)mem_tofree) {
         int j, k, i;
         static unsigned int next_db = 0;
         sds bestkey = NULL;