On 2019-11-13, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Tue, Nov 05, 2019 at 08:05:50PM +1100, Aleksa Sarai wrote: > > > One other possible alternative (which previous versions of this patch > > used) would be to check with path_is_under() if there was a racing > > rename or mount (after re-taking the relevant seqlocks). While this does > > work, it results in possible O(n*m) behaviour if there are many renames > > or mounts occuring *anywhere on the system*. > > BTW, do you realize that open-by-fhandle (or working nfsd, for that matter) > will trigger arseloads of write_seqlock(&rename_lock) simply on d_splice_alias() > bringing disconnected subtrees in contact with parent? I wasn't aware of that -- that makes path_is_under() even less viable. I'll reword it to be clearer that path_is_under() isn't a good idea and why we went with -EAGAIN over an in-kernel retry. -- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH <https://www.cyphar.com/>
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