Messages in this thread |  | | From | Linus Torvalds <> | Date | Sun, 15 Apr 2018 11:34:17 -0700 | Subject | Re: [PATCH] fs/dcache.c: re-add cond_resched() in shrink_dcache_parent() |
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On Sat, Apr 14, 2018 at 5:51 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: >> if (!list_empty(&data.select.found))
That was obviously meant to be just
if (data.select.found)
I had just cut-and-pasted a bit too much.
> You would have to do the same in check_and_drop() as well, > and that brings back d_invalidate()/d_invalidate() livelock > we used to have. See 81be24d263db...
Ugh. These are all really incestuous and very intertwined. Yes.
> I'm trying to put something together, but the damn thing is > full of potential livelocks, unfortunately ;-/ Will send > a followup once I have something resembling a sane solution...
Ok, that patch of yours looks like a nice cleanup, although *please* don't do this:
- struct detach_data *data = _data; - if (d_mountpoint(dentry)) { __dget_dlock(dentry); - data->mountpoint = dentry; + *(struct dentry **)_data = dentry;
Please keep the temporary variable, and make it do
+ struct dcache **victim = _victim; ... + *victim = dentry;
to kind of match the caller, which does
d_walk(dentry, &victim, find_submount);
because I abhor those casts inside code, and we have a pattern of passing 'void *_xyz' to callback functions and then making the right type by that kind of
struct right_type *xyz = _xyz;
at the very top of the function.
No, it's obviously not type-safe, but at least it's _legible_, and is a pattern, while that "let's randomly just do a cast in the middle of the code" is just nasty.
Side note: I do feel like "d_walk()" should be returning whether it terminated early or not. For example, this very same code in the caller does
+ struct dentry *victim = NULL; + d_walk(dentry, &victim, find_submount); + if (!victim) {
but in many ways it would be more natural to just check the exit condition, and
+ struct dentry *victim; + if (!d_walk(dentry, &victim, find_submount)) {
don't you think? Because that matches the actual setting condition in the find_submount() callback.
There are other situations where the same thing is true: that path_check_mount() currently has that "info->mounted" flag, but again, it could be replaced by just checking what the quit condition was, and whether we terminated early or not. Because the two are 100% equivalent, and the return value in many ways would be more logical, I feel.
(I'm not sure if we should just return the actual exit condition - defaulting to D_WALK_CONTINUE if there was nothing to walk at all - or whether we should just return a boolean for "terminated early")
Hmm?
Linus
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