ZSTD-DEBUG: Bypass custom allocators only in ASAN userspace builds

Use default malloc in userspace ASAN builds (zloop) to avoid memory
fragmentation issues. Custom allocators remain active in kernel and
non-ASAN userspace builds to preserve zdb compatibility.

This is a TEMPORARY DEBUG commit and must be replaced before merge.

Signed-off-by: Alexander Moch <mail@alexmoch.com>

Author: alex-moch

module/zstd/zfs_zstd.c

@@ -199,6 +199,26 @@ static const ZSTD_customMem zstd_dctx_malloc = {
 	NULL,
 };
 
+static inline ZSTD_CCtx *
+zfs_zstd_createCCtx(void)
+{
+#if !defined(_KERNEL) && defined(ZFS_ASAN_ENABLED)
+	return (ZSTD_createCCtx());
+#else
+	return (ZSTD_createCCtx_advanced(zstd_malloc));
+#endif
+}
+
+static inline ZSTD_DCtx *
+zfs_zstd_createDCtx(void)
+{
+#if !defined(_KERNEL) && defined(ZFS_ASAN_ENABLED)
+	return (ZSTD_createDCtx());
+#else
+	return (ZSTD_createDCtx_advanced(zstd_dctx_malloc));
+#endif
+}
+
 /* Level map for converting ZFS internal levels to ZSTD levels and vice versa */
 static struct zstd_levelmap zstd_levels[] = {
 	{ZIO_ZSTD_LEVEL_1, ZIO_ZSTD_LEVEL_1},
@@ -452,7 +472,7 @@ zfs_zstd_compress_impl(void *s_start, void *d_start, size_t s_len, size_t d_len,
 	ASSERT3U(d_len, <=, s_len);
 	ASSERT3U(zstd_level, !=, 0);
 
-	cctx = ZSTD_createCCtx_advanced(zstd_malloc);
+	cctx = zfs_zstd_createCCtx();
 
 	/*
 	 * Out of kernel memory, gently fall through - this will disable
@@ -646,7 +666,7 @@ zfs_zstd_decompress_level_buf(void *s_start, void *d_start, size_t s_len,
 		return (1);
 	}
 
-	dctx = ZSTD_createDCtx_advanced(zstd_dctx_malloc);
+	dctx = zfs_zstd_createDCtx();
 	if (!dctx) {
 		ZSTDSTAT_BUMP(zstd_stat_dec_alloc_fail);
 		return (1);