[PATCH] mmc: failure of block read wait for long time

Mon Sep 20 08:37:24 EDT 2010

> -----Original Message-----
> From: Adrian Hunter [mailto:adrian.hunter at nokia.com]
> Sent: Monday, September 20, 2010 5:20 PM
> To: Ghorai, Sukumar
> Cc: linux-mmc at vger.kernel.org; linux-arm-kernel at lists.infradead.org;
> Adrian Hunter
> Subject: Re: [PATCH] mmc: failure of block read wait for long time
> 
> On 20/09/10 11:57, Ghorai, Sukumar wrote:
> > Adrian,
> >
> >> -----Original Message-----
> >> From: Adrian Hunter [mailto:adrian.hunter at nokia.com]
> >> Sent: Monday, September 20, 2010 1:24 PM
> >> To: Ghorai, Sukumar
> >> Cc: linux-mmc at vger.kernel.org; linux-arm-kernel at lists.infradead.org;
> >> Adrian Hunter
> >> Subject: Re: [PATCH] mmc: failure of block read wait for long time
> >>
> >> On 14/09/10 08:15, ext Ghorai, Sukumar wrote:
> >>> Adrian,
> >>>
> >>> [..snip..]
> >>>>>>> [Ghorai] Adrian,
> >>>>>>> Yes this works and reduced the retry by 1/4 (2048 to 512 times for
> >> 1MB
> >>>>>> data read) form the original code;
> >>>>>>> Initially it was retrying for each page(512 bytes) after multi-
> block
> >>>>>> read fail; but this solution is retying for each segment(2048
> bytes);
> >>>>>>> 1. Now say block layrer reading 1MB and failed for the 1st segment.
> >> So
> >>>>>> it will still retry for 1MB/2048-bytes, i.e. 512 times.
> >>>>>>> 2. So do you think any good reason to retry again and again?
> >>>>>> If you have 1MB that is not readable, it sounds like the card is
> >> broken.
> >>>>>> Why are so many reads failing?  Has the card been removed?
> >>>>>>
> >>>>>> You might very rarely see ECC errors in a small number of sectors,
> >>>>>> but more than that sounds like something else is broken.
> >>>>>
> >>>>> [Ghorai] yes, one example is we remove the card when reading data,
> >>>>
> >>>> Well, that is a different case.  Once the card has gone, the block
> >> driver
> >>>> can (and will once the remove method is called) error out all I/O
> >>>> requests without sending them to MMC.  That doesn't happen until
> there
> >>>> is a card detect interrupt and a resulting rescan.
> >>>
> >>> [Ghorai] here we are discussing two problem,
> >>> 1. If IO failed how to stop retry; because of -
> >>> 	a. internal card error
> >>> 	b. issue in Filesystem, driver, or host controller issue
> >>> 	c. or cards removed.
> >>>
> >>> 2. And 2nd how to sync block-layer IO, if card removed,
> >>> 	a. case 1: when card removed interrupt support by the platform
> >>> 	b. case 2: when card removed interrupt does not support by the
> >> platform?
> >>>
> >>>>
> >>>> A possible solution is to put a flag on mmc_card to indicate
> card_gone
> >>>> that gets set as soon as the drivers card detect interrupt shows
> there
> >>>> is no card (hoping that we are not getting any bouncing on card
> detect)
> >>>> and then have mmc_wait_for_req() simple return -ENODEV immediately if
> >>>> the card_gone flag is set.  Finally, if the mmc block driver sees
> >>>> a -ENODEV error, it should also check the card_gone flag (via a new
> >>>> core function) and if the card is gone, do not retry - and perhaps
> >>>> even error out the rest of the I/O request queue as well.
> >>>
> >>> [Ghorai] your idea address the 2.a case, but not 2.b, 1.a, 1.b
> >>
> >> The card removal case can be extended to use the bus ops detect method
> >> when there is no card detect irq.  I will send a RFC patch.
> >>
> >> With respect to 1.a:
> >>    - If the card has an internal error, then it is broken.  The user
> >>    should remove the card and use a better one.  I do not see how
> reducing
> >>    retry delays really helps the user very much.  Arguably if the card
> >>    becomes unresponsive, the MMC core could provide a facility to
> >>    reinitialise the card, but that is yet another issue.
> >>
> >> With respect to 1.b:
> >>    - The file system cannot cause the block driver to have I/O errors.
> >>    - If there are errors in the driver they should be fixed.
> >>    - If there are hardware problems with the host controller, then
> >>    it is up to the host controller driver to deal with them e.g.
> >>    by resetting the controller.  I don't see what this has to do with
> >>    the block driver.
> >>
> >> You leave out the important case of ECC errors.  I am concerned about
> >> this because of the possibility that it happens inside a file system
> >> journal e.g. EXT4 journal.  Perhaps the journal may be recovered if the
> >> error only affects the last transaction, but perhaps not if it destroys
> >> other transactions - which could happen if the approach you suggest
> >> is taken.
> >>
> > [Ghorai] Thanks lot for your descriptive answer.
> > 1. Can you answer this? 2.b. case 2: when card removed interrupt does
> not support by the platform?
> 
> As I wrote above: The card removal case can be extended to use the bus ops
> detect method when there is no card detect irq.  I will send a RFC patch.
> 
> >
> > 2. Why block layer handling for inter-leave data? Can you give example
> diver who is returning interleave data? And how to tell application that
> buffer having interleave data?
> 
> I am not sure what you mean by interleave data, but file systems  for
> example
> are free to map any block to any file, directory or file system object,
> so a consecutive series of sectors may contain unrelated data.  Up to a
> maximum
> size, the block layer merges I/O requests when the sectors are consecutive,
> so an I/O request can also contain unrelated data.

[Ghorai] 
1. I don't think so, FS know where data exists and where is the free space. Except oth cluster.

2. Where its mentioned in block media that for segment-x[i],x[j] data read fail out of all all requested segments form [1..n].
And I never gone through any driver/protocol, that retry the next i+1th segment where ith-segment is failed. And for that my suggestion is preferred.

> 
> >
> >>>
> >>> And the solution I was proposing to return the status of IO failure as
> >> soon as possible to above layer; and handle the card removed interrupt
> >> separately or any other issue in h/w or s/w or combination of both. Or
> >> just think again when platform don't have the card remove interrupt.
> >>>
> >>> So my patch addresses the 1st part
> >>
> >> It is absolutely unacceptable to return I/O errors to the upper layers
> >> for segments that do not have errors.
> >>
> >>> And for the 2nd part we can submit the patch anytime.
> >>>
> >>>>
> >>>> I can suggest a patch if you want but I am on vacation next week so
> >>>> it will have to wait a couple of weeks.
> >>>>
> >>>>> And moreover we should not give the interleave data to apps, as we
> >> don't
> >>>> have option to tell application for the valid data.
> >>>>>
> >>> [..snip..]
> >>> http://comments.gmane.org/gmane.linux.kernel.mmc/2714
> >>>
> >>>>>
> >>>
> >>>
> >
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