linux-kernel - Re: [PATCH v3] scsi: NCR5380: Remove context check

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Date:   Tue, 8 Dec 2020 11:12:28 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     "Ahmed S. Darwish" <a.darwish@...utronix.de>
cc:     Michael Schmitz <schmitzmic@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Sebastian A. Siewior" <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] scsi: NCR5380: Remove context check

On Sun, 6 Dec 2020, Ahmed S. Darwish wrote:

> NCR5380_poll_politely2() uses in_interrupt() and irqs_disabled() to
> check if it is safe to sleep.
> 
> Such usage in drivers is phased out and Linus clearly requested that
> code which changes behaviour depending on context should either be
> separated, or the context be explicitly conveyed in an argument passed
> by the caller.
> 
> Below is a context analysis of NCR5380_poll_politely2() uppermost
> callers:
> 
>   - NCR5380_maybe_reset_bus(), task, invoked during device probe.
>     -> NCR5380_poll_politely()
>     -> do_abort()
> 
>   - NCR5380_select(), task, but can only sleep in the "release, then
>     re-acquire" regions of the spinlock held by its caller.
>     Sleeping invocations (lock released):
>     -> NCR5380_poll_politely2()
> 
>     Atomic invocations (lock acquired):
>     -> NCR5380_reselect()
>        -> NCR5380_poll_politely()
>        -> do_abort()
>        -> NCR5380_transfer_pio()
> 
>   - NCR5380_intr(), interrupt handler
>     -> NCR5380_dma_complete()
>        -> NCR5380_transfer_pio()
> 	  -> NCR5380_poll_politely()
>     -> NCR5380_reselect() (see above)
> 
>   - NCR5380_information_transfer(), task, but can only sleep in the
>     "release, then re-acquire" regions of the caller-held spinlock.
>     Sleeping invocations (lock released):
>       - NCR5380_transfer_pio() -> NCR5380_poll_politely()
>       - NCR5380_poll_politely()
> 
>     Atomic invocations (lock acquired):
>       - NCR5380_transfer_dma()
> 	-> NCR5380_dma_recv_setup()
>            => generic_NCR5380_precv() -> NCR5380_poll_politely()
> 	   => macscsi_pread() -> NCR5380_poll_politely()
> 
> 	-> NCR5380_dma_send_setup()
>  	   => generic_NCR5380_psend -> NCR5380_poll_politely2()
> 	   => macscsi_pwrite() -> NCR5380_poll_politely()
> 
> 	-> NCR5380_poll_politely2()
>         -> NCR5380_dma_complete()
>            -> NCR5380_transfer_pio()
> 	      -> NCR5380_poll_politely()
>       - NCR5380_transfer_pio() -> NCR5380_poll_politely
> 
>   - NCR5380_reselect(), atomic, always called with hostdata spinlock
>     held.
> 
> Since NCR5380_poll_politely2() already takes a "wait" argument in
> jiffies, use it to determine if the function can sleep. Modify atomic
> callers, which passed an unused wait value in terms of HZ, to pass zero.
> 
> Suggested-by: Finn Thain <fthain@...egraphics.com.au>
> Co-developed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Ahmed S. Darwish <a.darwish@...utronix.de>
> Cc: Michael Schmitz <schmitzmic@...il.com>
> Cc: <linux-m68k@...ts.linux-m68k.org>

Acked-by: Finn Thain <fthain@...egraphics.com.au>