[scudo] Fix the calculation of PushedBytesDelta (llvm#95177)

ChiaHungDuan · web-flow · commit cc04bbb2752a · 2024-06-11T14:52:28.000-07:00
BytesInBG is always greater or equal to BG-&gt;BytesInBGAtLastCheckpoint.

Note that the bug led to unnecessary attempts of page releasing and
doesn't have critical impact on the correctness.
diff --git a/compiler-rt/lib/scudo/standalone/primary64.h b/compiler-rt/lib/scudo/standalone/primary64.h
@@ -1392,7 +1392,7 @@ template <typename Config> class SizeClassAllocator64 {
         continue;
       }
 
-      const uptr PushedBytesDelta = BG->BytesInBGAtLastCheckpoint - BytesInBG;
+      const uptr PushedBytesDelta = BytesInBG - BG->BytesInBGAtLastCheckpoint;
 
       // Given the randomness property, we try to release the pages only if the
       // bytes used by free blocks exceed certain proportion of group size. Note

Original file line number	Diff line number	Diff line change
`@@ -1392,7 +1392,7 @@ template <typename Config> class SizeClassAllocator64 {`
`1392`	`1392`	`continue;`
`1393`	`1393`	`}`
`1394`	`1394`
`1395`		`- const uptr PushedBytesDelta = BG->BytesInBGAtLastCheckpoint - BytesInBG;`
	`1395`	`+ const uptr PushedBytesDelta = BytesInBG - BG->BytesInBGAtLastCheckpoint;`
`1396`	`1396`
`1397`	`1397`	`// Given the randomness property, we try to release the pages only if the`
`1398`	`1398`	`// bytes used by free blocks exceed certain proportion of group size. Note`