Re: 3.4.0-02580-g72c04af regression on sparc64 - partitions not recognized

[Dan Williams]

On Thu, May 24, 2012 at 12:42 AM, James Bottomley
<jejbbe@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 2012-05-23 at 19:22 -0700, Dan Williams wrote:
>> On Wed, 2012-05-23 at 23:56 +0100, James Bottomley wrote:
>> > On Wed, 2012-05-23 at 14:04 -0400, David Miller wrote:
>> > > From: Meelis Roos <mroos@xxxxxxxx>
>> > > Date: Wed, 23 May 2012 19:46:46 +0300 (EEST)
>> > >
>> > > CC:'ing interested parties.
>> > >
>> > > >> > Just tested 3.4.0-02580-g72c04af on about 10 machines. While most of
>> > > >> > them work (including 3 different sparc64 machines with real scsi disks),
>> > > >> > Sun Netra X1 with pata_ali and IDE disk consistently fails to boot. sda
>> > > >> > is recognized but no partitions. 3.3.0 works fine, as did something
>> > > >> > around 3.4-rc7 (plain 3.4 not tested yet). No other IDE machines tested
>> > > >> > yet since I have none with remote console at the moment.
>> > > >>
>> > > >> If 3.4.0-final is OK, start bisecting from v3.4.0 until 72c04af.  One
>> > > >> possibility could be the sparc64 NOBOOTMEM conversion that went into
>> > > >> the merge window.
>> > > >
>> > > > Bisecting leads to this commit:
>> > > >
>> > > > a7a20d103994fd760766e6c9d494daa569cbfe06 is the first bad commit
>> > > > commit a7a20d103994fd760766e6c9d494daa569cbfe06
>> > > > Author: Dan Williams <dan.j.williams@xxxxxxxxx>
>> > > > Date:   Thu Mar 22 17:05:11 2012 -0700
>> > > >
>> > > >     [SCSI] sd: limit the scope of the async probe domain
>> >
>> > My theory is that this is an init problem: The assumption in a lot of
>> > our code is that async_synchronize_full() waits for everything ... even
>> > the domain specific async schedules, which isn't true.
>> >
>> > The code in init that makes this assumption is wait_for_device_probe().
>> > There's also a fun async_synchronize_full() in init_post() that assumes
>> > it can free the init memory after, which would fail badly if anything in
>> > init used an async domain.
>> >
>> > So either we fix the assumptions or we can't use domain specific async
>> > schedules.
>> >
>>
>> Hm, we already have cases of code not trusting the semantics of
>> wait_for_device_probe(), especially as it relates to async scanning like
>> in kernel/power/hibernate.c:
>>
>>                 /*
>>                  * Some device discovery might still be in progress; we need
>>                  * to wait for this to finish.
>>                  */
>>                 wait_for_device_probe();
>>
>>                 if (resume_wait) {
>>                         while ((swsusp_resume_device = name_to_dev_t(resume_file)) == 0)
>>                                 msleep(10);
>>                         async_synchronize_full();
>>                 }
>>
>>                 /*
>>                  * We can't depend on SCSI devices being available after loading
>>                  * one of their modules until scsi_complete_async_scans() is
>>                  * called and the resume device usually is a SCSI one.
>>                  */
>>                 scsi_complete_async_scans();
>
> This is actually looks wrong: it works if SCSI is built in, but it's a
> nop if SCSI is a module (the nop function is gated by the else clause of
> #ifdef CONFIG_SCSI)
>
> Rafael, you added this not via the SCSI tree, is that the intention?
>
>> ...so it seems scsi_complete_async_scans() should take care to flush sd
>> probe actions as well... here is a test patch:
>>
>> --- snip ---
>>
>> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
>> index 8906557..05a92d3 100644
>> --- a/drivers/scsi/scsi_scan.c
>> +++ b/drivers/scsi/scsi_scan.c
>> @@ -141,13 +141,13 @@ struct async_scan_data {
>>   * started scanning after this function was called may or may not have
>>   * finished.
>>   */
>> -int scsi_complete_async_scans(void)
>> +static void __scsi_complete_async_scans(void)
>>  {
>>         struct async_scan_data *data;
>>
>>         do {
>>                 if (list_empty(&scanning_hosts))
>> -                       return 0;
>> +                       return;
>>                 /* If we can't get memory immediately, that's OK.  Just
>>                  * sleep a little.  Even if we never get memory, the async
>>                  * scans will finish eventually.
>> @@ -181,6 +181,13 @@ int scsi_complete_async_scans(void)
>>         spin_unlock(&async_scan_lock);
>>
>>         kfree(data);
>> +}
>> +
>> +int scsi_complete_async_scans(void)
>> +{
>> +       __scsi_complete_async_scans();
>> +       async_synchronize_full_domain(&scsi_sd_probe_domain);
>> +
>>         return 0;
>>  }
>
> But this still doesn't fix the boot problem, does it? ... unless we want
> to add a scsi_complete_async_scans() into init/do_mounts.c, which looks
> like piling one hack on top of another.

I managed to convince myself that one in prepare_namespace() was
probably not needed because of the late_initcall of
scsi_complete_async_scans() in the built-in case and in the module
case the initramfs should be taking care of it.

> I really think the correct fix is to have wait_for_device_probe()
> actually wait until all probes have completed and everything is
> discovered, that way we get the semantics the name implies and boot
> should just work.
>

...but wouldn't it need to go something like:

wait_for_device_probe(); /* all pci drivers probed */
scsi_complete_async_scans(): /* flush host scans */
wait_for_device_probe(); /* all recently attached sd devices probed */

?

--
Dan
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