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SubjectRe: [PATCH 02/11] vfs: More precise tests in d_invalidate
Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Sat, Feb 15, 2014 at 2:51 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> the whole check_submounts_and_drop thing walks the parent chain and
>> locks each parent with the renamelock held for writing.
>
> Oops, my bad about the write lock, brainfart due to grepping and
> reading the wrong context...
>
> check_submounts_and_drop() doesn't do the parent walk with the rename
> lock held for writing, it just holds it for reading.
>
> But it does do that very complex "walk parents and check all siblings"
> and locks them, so the rest of the commentary was correct.

Except that today d_invalidate drops the dcache lock and
calls shrink_dcache_parent. Which gets you into exactly the same
complex "walk parents and check all siblings" code.

The only difference between the shrink_dcache_parent and
check_submounts_and_drop (not counting the final drop)
is that check_submounts_and_drop aborts when it encounters a dentry
with d_mountpoint set.


So no I am not trying to hide something. I called out that I changed
this logic in particular and this particular patch all I am doing is
killing the enforcing of 2.2 era logic. Further I front loaded this
change so I bisect could point it's fingers at this before any other
substantial changes were made if this is indeed a problem.

Beyond that check_submounts_and_drop is what well maintained distributed
filesystems are calling from d_revalidate.


Now I would not be surprised if this change to d_invalidate is a
challenge to get your head around. It took me a while of reading the
code to realize (a) how the code makes some degree of sense today,
and (b) that the change is semantically safe.


But when shrink_dcache_parent and check_submounts_and_drop are
effectiely the same function I can't possibly see how you can argue how
the locking has changed or that I am trying to hide things.

Eric


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