From: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
To: linux-mm@kvack.org
Subject: Question: why hold source mm->mmap_sem write sem in dup_mmap()?
Date: Fri, 29 Sep 2006 18:02:16 -0700 [thread overview]
Message-ID: <000301c6e42c$12a62490$ff0da8c0@amr.corp.intel.com> (raw)
In the call chain of copy_page_range coming from do_fork(), dup_mmap holds
write semaphore on the oldmm. I don't see copy_page_range() or dup_mmap
itself alter the source (oldmm)'s address space, what is the reason to hold
write semaphore on the source mm? Won't a down_read(&oldmm->mmap_sem) be
sufficient? Did I miss something there?
do_fork
copy_process
copy_mm
dup_mm
dup_mmap
copy_page_range
static inline int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
{
...
down_write(&oldmm->mmap_sem);
flush_cache_mm(oldmm);
down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
...
for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
...
retval = copy_page_range(mm, oldmm, mpnt);
}
...
up_write(&mm->mmap_sem);
flush_tlb_mm(oldmm);
up_write(&oldmm->mmap_sem);
}
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next reply other threads:[~2006-09-30 1:02 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-30 1:02 Chen, Kenneth W [this message]
2006-09-30 14:45 ` Hugh Dickins
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