[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] xen/events: Fix race in set_evtchn_to_irq
On Wed, 2021-08-11 at 11:05 -0400, Boris Ostrovsky wrote: > On 8/11/21 10:08 AM, Maximilian Heyne wrote: > > This patch sets evtchn_to_irq rows via a cmpxchg operation so that > > they > > will be set only once. Clearing the row was moved up before writing > > the > > row to evtchn_to_irq in order to not create a race once the row is > > visible for other threads. Accesses to the rows are now guarded by > > READ_ONCE and WRITE_ONCE just as for the columns in the data > > structure. > > Is this last part really needed? We needed to do that for array > elements to avoid an interrupt handler from seeing a partially > updated entry but I am not sure I see how this can happen to the row > pointer. The only place where it might be important is when we update > the pointer to the new page but you are using cmpxchg there already. I think you are right. I will remove the changes related to the READ_ONCE. > > > > - evtchn_to_irq[row] = (int > > *)get_zeroed_page(GFP_KERNEL); > > - if (evtchn_to_irq[row] == NULL) > > + evtchn_row = (int *) get_zeroed_page(GFP_KERNEL); > > Not directly related to this patch but I don't think we need to get a > zeroed page --- we will initialize it to -1 immediately below. That is correct. I will just fix this in the next version of the patch. Max Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
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