Messages in this thread | | | Date | Tue, 11 Sep 2018 14:02:58 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCHv3 6/6] tty/ldsem: Decrement wait_readers on timeouted down_read() |
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On Tue, Sep 11, 2018 at 02:48:21AM +0100, Dmitry Safonov wrote: > It seems like when ldsem_down_read() fails with timeout, it misses > update for sem->wait_readers. By that reason, when writer finally > releases write end of the semaphore __ldsem_wake_readers() does adjust > sem->count with wrong value: > sem->wait_readers * (LDSEM_ACTIVE_BIAS - LDSEM_WAIT_BIAS) > > I.e, if update comes with 1 missed wait_readers decrement, sem->count > will be 0x100000001 which means that there is active reader and it'll > make any further writer to fail in acquiring the semaphore. > > It looks like, this is a dead-code, because ldsem_down_read() is never > called with timeout different than MAX_SCHEDULE_TIMEOUT, so it might be > worth to delete timeout parameter and error path fall-back..
You might want to think about ditching that ldsem thing entirely, and use a regular rwsem ?
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