From 6b454989853075b1bd757c3f1764e366b8b00489 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=9B=D0=B5=D0=BE=D0=BD=D0=B8=D0=B4=20=D0=AE=D1=80=D1=8C?=
 =?UTF-8?q?=D0=B5=D0=B2=20=28Leonid=20Yuriev=29?= <leo@yuriev.ru>
Date: Tue, 22 Feb 2022 23:48:58 +0300
Subject: [PATCH] mdbx: temporary workaround/hotfix for a flaw of Linux 4.19
 (at least) unified page/buffer cache.

Temporary workaround for https://github.com/erthink/libmdbx/issues/269.
---
 src/core.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/src/core.c b/src/core.c
index 4f7b9b8a..5c836258 100644
--- a/src/core.c
+++ b/src/core.c
@@ -12780,6 +12780,22 @@ __cold int mdbx_env_open(MDBX_env *env, const char *pathname,
         goto bailout;
       }
     }
+#elif defined(__linux__) || defined(__gnu_linux__)
+    /* Temporary workaround for Linux 4.19 (at least) kernel's flaw.
+     * See https://github.com/erthink/libmdbx/issues/269 */
+    if ((flags & MDBX_WRITEMAP) == 0 &&
+        mdbx_linux_kernel_version < 0x05040000) {
+      if (flags & MDBX_ACCEDE)
+        flags |= MDBX_WRITEMAP;
+      else {
+        mdbx_debug_log(MDBX_LOG_ERROR, __func__, __LINE__,
+                       "Linux prior to 5.4 requires MDBX_WRITEMAP because "
+                       "of a flaw of unified page/buffer cache. "
+                       "See https://github.com/erthink/libmdbx/issues/269\n");
+        rc = ENOPROTOOPT;
+        goto bailout;
+      }
+    }
 #endif /* MDBX_MMAP_INCOHERENT_FILE_WRITE */
   }