On Sat, 2017-09-09 at 19:31 +0100, Al Viro wrote: > On Sat, Sep 09, 2017 at 06:03:16PM +0530, Gargi Sharma wrote: > > If a task exits before procfs is mounted, proc_flush_task_mnt will > > be called with a NULL mnt parameter. In that case, not only is > > there > > nothing to unhash, but trying to do so will oops the kernel with a > > null pointer dereference. > > You are misreading that sucker. It's about userland mounts, it's > about > the internal ones in pidns, for each pidns the process belongs to. > > IOW, what you are adding is dead code. The very first alloc_pid() in > that pidns should've called pid_ns_prepare_proc(), which creates that > vfsmount.
Looking at the code (now that I am home, and no longer reading this email on my phone), I see the cause of this problem. A previous version of Gargi's code had RESERVED_PIDS as the lower bound for idr_alloc_cyclic, even on the very first PID allocation cycle in a PID namespace. With the code changed to have 1 as the lower bound during the first allocation cycle, pid_ns_prepare_proc() should be called correctly, and things should work as expected. Gargi, can you drop this patch 1/2, and make sure the code still works fine? -- All Rights Reversed.
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