Messages in this thread | | | Date | Wed, 17 Apr 2019 12:26:56 -0700 | From | Tejun Heo <> | Subject | Re: [PATCH RFC 1/1] kernfs: keep kernfs node alive for __kernfs_remove() |
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Hello,
On Wed, Apr 17, 2019 at 04:12:29PM +0000, Konstantin Khorenko wrote: > i don't know the full scenario unfortunately, but the idea is the following: > > __kernfs_remove() is called under kernfs_mutex and if > !(!kn || (kn->parent && RB_EMPTY_NODE(&kn->rb))) > > it assumes that nothing can change while we hold the mutex and > for each kernfs descendant should have kn->count > 0. > > ===== > /* deactivate and unlink the subtree node-by-node */ > do { > pos = kernfs_leftmost_descendant(kn); > > /* > * kernfs_drain() drops kernfs_mutex temporarily and @pos's > * base ref could have been put by someone else by the time > * the function returns. Make sure it doesn't go away > * underneath us. > */ > kernfs_get(pos); > ===== > > At the same time kernfs_notify_workfn() can do a kernfs_put() out of kernfs_mutex > which probably can be the last put and dec kn->count to 0 any moment.
Yeah, but the caller of __kernfs_remove() should be holding the ref, so I don't see how it'd reach zero. Also, just putting that one kernfs_put() inside mutex can't possibly be the right solution given that the function is allowed to be called from any context. I think we need to understand what's going on better before making changes.
Thanks.
-- tejun
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