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get_user_pages_unlocked(): pass true to __get_user_pages_locked() notify_drop 

Equivalent transformation - the only place in __get_user_pages_locked()
where we look at notify_drop argument is
	if (notify_drop && lock_dropped && *locked) {
		up_read(&mm->mmap_sem);
		*locked = 0;
	}
in the very end.  Changing notify_drop from false to true won't change
behaviour unless *locked is non-zero.  The caller is
        ret = __get_user_pages_locked(current, mm, start, nr_pages, pages, NULL,
			      &locked, false, gup_flags | FOLL_TOUCH);
	if (locked)
		up_read(&mm->mmap_sem);
so in that case the original kernel would have done up_read() right after
return from __get_user_pages_locked(), while the modified one would've done
it right before the return.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2017-11-19 11:21:10 -05:00
parent 9a949e8ff9
commit 14cb138d7c
1 changed files with 1 additions and 1 deletions
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2
mm/gup.c
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@ -988,7 +988,7 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
down_read(&mm->mmap_sem);
ret = __get_user_pages_locked(current, mm, start, nr_pages, pages, NULL,
&locked, false, gup_flags | FOLL_TOUCH);
&locked, true, gup_flags | FOLL_TOUCH);
if (locked)
up_read(&mm->mmap_sem);
return ret;