On Tue, Jul 30, 2019 at 11:55 AM J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > On Tue, Jul 30, 2019 at 11:48:27AM -0400, Olga Kornievskaia wrote: > > On Tue, Jul 23, 2019 at 4:46 PM J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > > > > > On Mon, Jul 22, 2019 at 04:17:44PM -0400, Olga Kornievskaia wrote: > > > > Let me see if I understand your suspicion and ask for guidance how to > > > > resolve it as perhaps I'm misusing the function. idr_alloc_cyclic() > > > > keeps track of the structure of the 2nd arguments with a value it > > > > returns. How do I initiate the structure with the value of the > > > > function without knowing the value which can only be returned when I > > > > call the function to add it to the list? what you are suggesting is to > > > > somehow get the value for the new_id but not associate anything then > > > > update the copy structure with that value and then call > > > > idr_alloc_cyclic() (or something else) to create that association of > > > > the new_id and the structure? I don't know how to do that. > > > > > > You could move the initialization under the s2s_cp_lock. But there's > > > additional initialization that's done in the caller. > > > > I still don't understand what you are looking for here and why. I'm > > following what the normal stid allocation does. There is no extra code > > there to see if it initiated or not. nfs4_alloc_stid() calls > > idr_alloc_cyclic() creates an association between the stid pointer and > > at the time uninitialized nfs4_stid structure which is then filled in > > with the return of the idr_alloc_cyclic(). That's exactly what the new > > code is doing (well accept that i'll change it to store the > > stateid_t). > > Yes, I'm a little worried about normal stid allocation too. It's got > one extra safeguard because of the check for 0 sc_type in the lookup, > I haven't yet convinced myself that's enough. > > The race I'm worried about is: one task does the idr allocation and > drops locks. Before it has the chance to finish initializing the > object, a second task looks it up in the idr and does something with it. > It sees the not-yet-initialized fields. Can the spin_lock() that we call before the idr_alloc_cyclic() be held thru the initialization of the stid then? I'm just not sure what this idr_preload_end() with a spin_lock but otherwise I don't see why we can't and since idr_find() takes the same spin lock before the call, it would solve the problem. > > --b.
