Hi, On Tue, Sep 19, 2017 at 1:37 PM, Oliver Neukum <oneukum@xxxxxxxx> wrote: > Am Dienstag, den 19.09.2017, 09:15 -0700 schrieb Douglas Anderson: >> In general when you've got a flag communicating that "something needs >> to be done" you want to clear that flag _before_ doing the task. If >> you clear the flag _after_ doing the task you end up with the risk >> that this will happen: >> >> 1. Requester sets flag saying task A needs to be done. >> 2. Worker comes and stars doing task A. >> 3. Worker finishes task A but hasn't yet cleared the flag. >> 4. Requester wants to set flag saying task A needs to be done again. >> 5. Worker clears the flag without doing anything. >> >> Let's make the usbnet codebase consistently clear the flag _before_ it >> does the requested work. That way if there's another request to do >> the work while the work is already in progress it won't be lost. >> >> NOTES: >> - No known bugs are fixed by this; it's just found by code inspection. > > Hi, > > unfortunately the patch is wrong. The flags must be cleared only > in case the handler is successful. That is not guaranteed. > > Regards > Oliver > > NACK OK, thanks for reviewing! I definitely wasn't super confident about the patch (hence the RFC). Do you think that the races I identified are possible to hit? In other words: should I try to rework the patch somehow or just drop it? Originally I had the patch setting the flags back to true in the failure cases, but then I convinced myself that wasn't needed. I can certainly go back and try it that way... -Doug -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
