linux-kernel - [PATCH] arch: um: kernel: skas: mmu: remove pmd_free() and pud_free() for failure processing in init_stub

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Date:	Wed, 13 Nov 2013 13:06:48 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Jeff Dike <jdike@...toit.com>, Richard Weinberger <richard@....at>
CC:	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	uml-devel <user-mode-linux-devel@...ts.sourceforge.net>,
	uml-user <user-mode-linux-user@...ts.sourceforge.net>
Subject: [PATCH] arch: um: kernel: skas: mmu: remove pmd_free() and pud_free()
 for failure processing in init_stub_pte()

Unfortunately, p?d_alloc() and p?d_free() are not pair!! If p?d_alloc()
succeed, they may be used, so in the next failure, we have to skip them
to let exit_mmap() or do_munmap() to process it.

According to "Documentation/vm/locking", 'mm->page_table_lock' is for
using vma list, so not need it when its related vmas are detached or
unmapped from using vma list.

The related work flow:

  exit_mmap() ->
    unmap_vmas(); /* so not need mm->page_table_lock */
    free_pgtables();

  do_munmap()->
    detach_vmas_to_be_unmapped(); /* so not need mm->page_table_lock */
    unmap_region() ->
      free_pgtables();

  free_pgtables() ->
    free_pgd_range() ->
      free_pud_range() ->
        free_pmd_range() ->
          free_pte_range() ->
            pmd_clear();
            pte_free_tlb();
          pud_clear();
          pmd_free_tlb();
        pgd_clear(); 
        pud_free_tlb();


Signed-off-by: Chen Gang <gang.chen@...anux.com>
---
 arch/um/kernel/skas/mmu.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index 007d550..3fd1951 100644
--- a/arch/um/kernel/skas/mmu.c
+++ b/arch/um/kernel/skas/mmu.c
@@ -40,9 +40,9 @@ static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
 	return 0;
 
  out_pte:
-	pmd_free(mm, pmd);
+	/* used by mm->pgd->pud, will free in do_munmap() or exit_mmap() */
  out_pmd:
-	pud_free(mm, pud);
+	/* used by mm->pgd, will free in do_munmap() or exit_mmap() */
  out:
 	return -ENOMEM;
 }
-- 
1.7.7.6
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