From: Hugh Dickins Date: Sun, 30 Oct 2005 01:16:08 +0000 (-0700) Subject: [PATCH] mm: dup_mmap down new mmap_sem X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=7ee78232501ea9de2b6c8f10d32c9a0fee541357;p=GitHub%2FLineageOS%2Fandroid_kernel_samsung_universal7580.git [PATCH] mm: dup_mmap down new mmap_sem 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/fork.c b/kernel/fork.c index 0e7fe4a8a8d..2a587b3224e 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -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;