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Message-ID: <1332340575.12353.55.camel@deneb.redhat.com>
Date: Wed, 21 Mar 2012 10:36:14 -0400
From: Mark Salter <msalter@...hat.com>
To: aarcange@...hat.com
Cc: linux-kernel <linux-kernel@...r.kernel.org>,
linux-next <linux-next@...r.kernel.org>
Subject: build failure in linux-next
I'm seeing a build failure in linux-next:
CC init/main.o
In file included from /es/linux/linux-next/arch/c6x/include/asm/pgtable.h:76:0,
from /es/linux/linux-next/include/linux/mm.h:44,
from /es/linux/linux-next/include/linux/ring_buffer.h:5,
from /es/linux/linux-next/include/linux/ftrace_event.h:4,
from /es/linux/linux-next/include/trace/syscall.h:6,
from /es/linux/linux-next/include/linux/syscalls.h:78,
from /es/linux/linux-next/init/main.c:16:
/es/linux/linux-next/include/asm-generic/pgtable.h: In function 'pmd_none_or_trans_huge_or_clear_bad':
/es/linux/linux-next/include/asm-generic/pgtable.h:476:4: error: implicit declaration of function 'pmd_clear_bad' [-Werror=implicit-function-declaration]
This patch added some functions to asm-generic/pgtable.h which should
have been placed in the CONFIG_MMU conditional block:
Author: Andrea Arcangeli <aarcange@...hat.com>
Date: Wed Mar 21 10:48:00 2012 +1100
mm: thp: fix pmd_bad() triggering in code paths holding mmap_sem read mode
The following patch fixes the build problem for me:
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 202c010..8ba3ba5 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -342,6 +342,64 @@ static inline void ptep_modify_prot_commit(struct mm_struct *mm,
__ptep_modify_prot_commit(mm, addr, ptep, pte);
}
#endif /* __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION */
+
+/*
+ * This function is meant to be used by sites walking pagetables with
+ * the mmap_sem hold in read mode to protect against MADV_DONTNEED and
+ * transhuge page faults. MADV_DONTNEED can convert a transhuge pmd
+ * into a null pmd and the transhuge page fault can convert a null pmd
+ * into an hugepmd or into a regular pmd (if the hugepage allocation
+ * fails). While holding the mmap_sem in read mode the pmd becomes
+ * stable and stops changing under us only if it's not null and not a
+ * transhuge pmd. When those races occurs and this function makes a
+ * difference vs the standard pmd_none_or_clear_bad, the result is
+ * undefined so behaving like if the pmd was none is safe (because it
+ * can return none anyway). The compiler level barrier() is critically
+ * important to compute the two checks atomically on the same pmdval.
+ */
+static inline int pmd_none_or_trans_huge_or_clear_bad(pmd_t *pmd)
+{
+ /* depend on compiler for an atomic pmd read */
+ pmd_t pmdval = *pmd;
+ /*
+ * The barrier will stabilize the pmdval in a register or on
+ * the stack so that it will stop changing under the code.
+ */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ barrier();
+#endif
+ if (pmd_none(pmdval))
+ return 1;
+ if (unlikely(pmd_bad(pmdval))) {
+ if (!pmd_trans_huge(pmdval))
+ pmd_clear_bad(pmd);
+ return 1;
+ }
+ return 0;
+}
+
+/*
+ * This is a noop if Transparent Hugepage Support is not built into
+ * the kernel. Otherwise it is equivalent to
+ * pmd_none_or_trans_huge_or_clear_bad(), and shall only be called in
+ * places that already verified the pmd is not none and they want to
+ * walk ptes while holding the mmap sem in read mode (write mode don't
+ * need this). If THP is not enabled, the pmd can't go away under the
+ * code even if MADV_DONTNEED runs, but if THP is enabled we need to
+ * run a pmd_trans_unstable before walking the ptes after
+ * split_huge_page_pmd returns (because it may have run when the pmd
+ * become null, but then a page fault can map in a THP and not a
+ * regular page).
+ */
+static inline int pmd_trans_unstable(pmd_t *pmd)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ return pmd_none_or_trans_huge_or_clear_bad(pmd);
+#else
+ return 0;
+#endif
+}
+
#endif /* CONFIG_MMU */
/*
@@ -444,63 +502,6 @@ static inline int pmd_write(pmd_t pmd)
#endif /* __HAVE_ARCH_PMD_WRITE */
#endif
-/*
- * This function is meant to be used by sites walking pagetables with
- * the mmap_sem hold in read mode to protect against MADV_DONTNEED and
- * transhuge page faults. MADV_DONTNEED can convert a transhuge pmd
- * into a null pmd and the transhuge page fault can convert a null pmd
- * into an hugepmd or into a regular pmd (if the hugepage allocation
- * fails). While holding the mmap_sem in read mode the pmd becomes
- * stable and stops changing under us only if it's not null and not a
- * transhuge pmd. When those races occurs and this function makes a
- * difference vs the standard pmd_none_or_clear_bad, the result is
- * undefined so behaving like if the pmd was none is safe (because it
- * can return none anyway). The compiler level barrier() is critically
- * important to compute the two checks atomically on the same pmdval.
- */
-static inline int pmd_none_or_trans_huge_or_clear_bad(pmd_t *pmd)
-{
- /* depend on compiler for an atomic pmd read */
- pmd_t pmdval = *pmd;
- /*
- * The barrier will stabilize the pmdval in a register or on
- * the stack so that it will stop changing under the code.
- */
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- barrier();
-#endif
- if (pmd_none(pmdval))
- return 1;
- if (unlikely(pmd_bad(pmdval))) {
- if (!pmd_trans_huge(pmdval))
- pmd_clear_bad(pmd);
- return 1;
- }
- return 0;
-}
-
-/*
- * This is a noop if Transparent Hugepage Support is not built into
- * the kernel. Otherwise it is equivalent to
- * pmd_none_or_trans_huge_or_clear_bad(), and shall only be called in
- * places that already verified the pmd is not none and they want to
- * walk ptes while holding the mmap sem in read mode (write mode don't
- * need this). If THP is not enabled, the pmd can't go away under the
- * code even if MADV_DONTNEED runs, but if THP is enabled we need to
- * run a pmd_trans_unstable before walking the ptes after
- * split_huge_page_pmd returns (because it may have run when the pmd
- * become null, but then a page fault can map in a THP and not a
- * regular page).
- */
-static inline int pmd_trans_unstable(pmd_t *pmd)
-{
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- return pmd_none_or_trans_huge_or_clear_bad(pmd);
-#else
- return 0;
-#endif
-}
-
#endif /* !__ASSEMBLY__ */
#endif /* _ASM_GENERIC_PGTABLE_H */
--
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