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Currently d_move(from, to) does the following: * name/parent of from <- old name/parent of to, from hashed there * to is unhashed * name of to is preserved * if from used to be detached, to gets detached * if from used to be attached, parent of to <- old parent of from. That's both user-visibly bogus and complicates reasoning a lot. Much saner semantics would be * name/parent of from <- name/parent of to, from hashed there. * to is unhashed * name/parent of to is unchanged. The price, of course, is that old parent of from might lose a reference. However, * all potentially cross-directory callers of d_move() have both parents pinned directly; typically, dentries themselves are grabbed only after we have grabbed and locked both parents. IOW, the decrement of old parent's refcount in case of d_move() won't reach zero. * __d_move() from d_splice_alias() is done to detached alias. No refcount decrements in that case * __d_move() from __d_unalias() *can* get the refcount to zero. So let's grab a reference to alias' old parent before calling __d_unalias() and dput() it after we'd dropped rename_lock. That does make d_splice_alias() potentially blocking. However, it has no callers in non-sleepable contexts (and the case where we'd grown that dget/dput pair is _very_ rare, so performance is not an issue). Another thing that needs adjustment is unlocking in the end of __d_move(); folded it in. And cleaned the remnants of bogus ordering from the "lock them in the beginning" counterpart - it's never been right and now (well, for 7 years now) we have that thing always serialized on rename_lock anyway. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.