[PATCH v2] thp: Disable THP if THP isn't supported by kernel

From 99ddd2f374b9229c01b03a80b22ba454967e6ebe Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <[email protected]>
Date: Sat, 4 Jul 2026 08:17:05 +0800
Subject: [PATCH v2] thp: Disable THP if THP isn't supported by kernel

Since DL_MAP_DEFAULT_THP_PAGESIZE is defined for x86-64, THP control
is to set to madvise by default.  If THP is disabled in x86-64 kernel,
madvise (..., MADV_HUGEPAGE) returns -EINVAL to indicate that THP isn't
supported.  Add _dl_thp_madvise to disable THP in this case.  This
fixes BZ #34348.

Signed-off-by: H.J. Lu <[email protected]>
---
 sysdeps/unix/sysv/linux/dl-exec-post.h   |  6 ++--
 sysdeps/unix/sysv/linux/dl-load-post.h   |  6 ++--
 sysdeps/unix/sysv/linux/dl-thp-madvise.h | 41 ++++++++++++++++++++++++
 3 files changed, 49 insertions(+), 4 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/dl-thp-madvise.h

diff --git a/sysdeps/unix/sysv/linux/dl-exec-post.h b/sysdeps/unix/sysv/linux/dl-exec-post.h
index 9a49486db2..4bc8a50dd1 100644
--- a/sysdeps/unix/sysv/linux/dl-exec-post.h
+++ b/sysdeps/unix/sysv/linux/dl-exec-post.h
@@ -17,6 +17,8 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+#include "dl-thp-madvise.h"
+
 static inline void
 _dl_get_thp_config (void)
 {
@@ -116,8 +118,8 @@ _dl_executable_postprocess (struct link_map *main_map,
 	&& ((ph->p_vaddr | ph->p_offset) & (thp_pagesize - 1)) == 0
 	&& (ph->p_flags & (PF_W | PF_R)) == PF_R)
       {
-	int ret = __madvise ((void *) (main_map->l_addr + ph->p_vaddr),
-			     ph->p_memsz, MADV_HUGEPAGE);
+	void *addr = (void *) (main_map->l_addr + ph->p_vaddr);
+	int ret = _dl_thp_madvise (addr, ph->p_memsz);
 	if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_FILES))
 	  _dl_debug_printf ("\
 madvise (0x%0*lx, 0x%0*lx, MADV_HUGEPAGE) returns %d\n",
diff --git a/sysdeps/unix/sysv/linux/dl-load-post.h b/sysdeps/unix/sysv/linux/dl-load-post.h
index 741c4ddcb1..935298bda5 100644
--- a/sysdeps/unix/sysv/linux/dl-load-post.h
+++ b/sysdeps/unix/sysv/linux/dl-load-post.h
@@ -17,6 +17,8 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+#include "dl-thp-madvise.h"
+
 static bool _dl_segment_thp_eligible (const struct loadcmd *, size_t);
 
 /* After L has been mapped in, call madvise with MADV_HUGEPAGE for THP
@@ -28,8 +30,8 @@ _dl_postprocess_loadcmd_extra (struct link_map *l, const struct loadcmd *c)
   if (GL(dl_thp_mode) == thp_mode_madvise
       && _dl_segment_thp_eligible (c, GL(dl_elf_thp_pagesize)))
     {
-      int ret = __madvise ((void *) (l->l_addr + c->mapstart),
-			   c->mapend - c->mapstart, MADV_HUGEPAGE);
+      int ret = _dl_thp_madvise ((void *) (l->l_addr + c->mapstart),
+				 c->mapend - c->mapstart);
       if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_FILES))
 	_dl_debug_printf ("\
   madvise (0x%0*lx, 0x%0*lx, MADV_HUGEPAGE) returns %d\n",
diff --git a/sysdeps/unix/sysv/linux/dl-thp-madvise.h b/sysdeps/unix/sysv/linux/dl-thp-madvise.h
new file mode 100644
index 0000000000..d674a7d1c9
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/dl-thp-madvise.h
@@ -0,0 +1,41 @@
+/* _dl_thp_madvise.  Linux version.
+   Copyright (C) 2026 Free Software Foundation, Inc.
+   Copyright The GNU Toolchain Authors.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _DL_THP_MADVISE_H
+#define _DL_THP_MADVISE_H
+
+/* Similar to madvise, but disable THP if the madvise syscall returns
+   -EINVAL which indicates that THP isn't supported by kernel.  */
+
+static inline int
+_dl_thp_madvise (void *addr, size_t size)
+{
+  int res = INTERNAL_SYSCALL_CALL (madvise, addr, size, MADV_HUGEPAGE);
+  if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (res))
+      && INTERNAL_SYSCALL_ERRNO (res) == EINVAL)
+    {
+      /* NB: Disable THP if THP isn't supported by kernel.  */
+      GL(dl_thp_mode) = thp_mode_not_supported;
+      GL(dl_elf_thp_control) = dl_elf_thp_control_disabled;
+      return INTERNAL_SYSCALL_ERRNO (res);
+    }
+  return res;
+}
+
+#endif /* _DL_THP_MADVISE_H  */
-- 
2.55.0