On Mon, Oct 08, 2018 at 07:02:09PM +0200, Ahmad Fatoum wrote: > Hello, > > On 10/8/18 6:55 PM, Al Viro wrote: > > > > What the hell does that have to do with negative dentries anywhere??? > > It's possible that this needs fixing at another place. I don't know, > but this seems to work for me, that's why I prefixed with RFC.
OK, to elaborate: where have you seen negative dentries on procfs in the first place? I'm trying to find a way for such to happen, but I don't see any. And in any case, these ->d_delete() and ->d_revalidate() instances would've been oopsing on such. ->d_delete() is about retaining _unused_ dentries in hash for future lookups; nothing to do with positive/negative. *And* ->d_delete() is called only when refcount hits zero. If another process opens the damn thing and keeps it opened, ->d_delete() won't be called at all and your patch won't change the behaviour of the entire thing. If anything, you might want to have separate ->d_op for /proc/*/net, so that its ->d_revalidate() would return 0 if netns doesn't match. Would need a way to keep some information allowing to detect the switchover, of course (either in PROC_I(inode) or in ->d_fsdata of that dentry - in the latter case you'd want to do whatever you need to dispose of that in ->d_release()). Check in revalidate should be along the lines of "do what's currently done in get_proc_task_net(), compare the result with the memorized value, bugger off on mismatch", perhaps with memorized value being counted as a reference (in which case you'd want to do put_net() when disposing of the inode or dentry, whichever you use to keep it in). In that case proc_tgid_net_lookup()/proc_tgid_net_getattr()/proc_tgid_net_readdir() would simply use the stored reference instead of messing with get_proc_task_net() and put_net(). You'd need separate dentry_operations for /proc/*/net and /proc/*/*/net, instead of using pid_dentry_operations. That would need to be recognized in proc_pident_instantiate() (_without_ memcmp(p->name, "net", 4) on each call of that thing, preferably). I'd put that new instance of dentry_operations (along with the methods in it, of course) into fs/proc/proc_net.c, where we already have the inode and file methods of /proc/*/net.
