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[PATCH] mm: dup_mmap down new mmap_sem

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One anomaly remains from when Andrea rationalized the responsibilities of
mmap_sem and page_table_lock: in dup_mmap we add vmas to the child holding its
page_table_lock, but not the mmap_sem which normally guards the vma list and
rbtree.  Which could be an issue for unuse_mm: though since it just walks down
the list (today with page_table_lock, tomorrow not), it's probably okay.  Will
need a memory barrier?  Oh, keep it simple, Nick and I agreed, no harm in
taking child's mmap_sem here.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Hugh Dickins 2005-10-29 18:16:08 -07:00 committed by Linus Torvalds
parent fd3e42fcc8
commit 7ee7823250
1 changed files with 4 additions and 5 deletions
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9
kernel/fork.c
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@ -192,6 +192,8 @@ static inline int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
down_write(&oldmm->mmap_sem);
flush_cache_mm(oldmm);
down_write(&mm->mmap_sem);
mm->locked_vm = 0;
mm->mmap = NULL;
mm->mmap_cache = NULL;
@ -251,10 +253,7 @@ static inline int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
}
/*
* Link in the new vma and copy the page table entries:
* link in first so that swapoff can see swap entries.
* Note that, exceptionally, here the vma is inserted
* without holding mm->mmap_sem.
* Link in the new vma and copy the page table entries.
*/
spin_lock(&mm->page_table_lock);
*pprev = tmp;
@ -275,8 +274,8 @@ static inline int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
goto out;
}
retval = 0;
out:
up_write(&mm->mmap_sem);
flush_tlb_mm(oldmm);
up_write(&oldmm->mmap_sem);
return retval;