On 02/24, Andrei Vagin wrote: > > On Tue, Feb 24, 2026 at 5:38 AM Pavel Tikhomirov > > > > This check here is more for the concurrent alloc_pid() case. When one > > process > > in alloc_pid() successfully allocated the pid and than, for instance, hit > > the > > pidfs_add_pid() error and is going to free_pid(), but the pid 1 is remains > > yet > > allocated from idr and the cursor is on 2 at the moment. At the same time > > the > > concurrent process may get to alloc_pid(), and will see cursor on 2, it > > should > > not be able to create a process as this process will get pid 2 and will be > > created before init. > > > > And in general (non concurrent case) it makes sense to only allow > > allocating 1, > > for the first process. > > In this case, there is likely a race condition. Two alloc_pid() calls > can run concurrently, > where idr_get_cursor() returns 0 in both instances.
This code runs with pidmap_lock held. But, > I think this > check needs to > be moved after idr_alloc_cyclic() to verify the actual value that was > allocated. Agreed, see other emails in this thread. Oleg.
