RE: [PATCH RESEND v6 1/9] pagemap: Introduce ->memory_failure()

-----Original Message-----
From: Jane Chu <redacted>
Subject: Re: [PATCH RESEND v6 1/9] pagemap: Introduce ->memory_failure()


On 8/17/2021 10:43 PM, Jane Chu wrote:

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More information -

On 8/16/2021 10:20 AM, Jane Chu wrote:

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Hi, ShiYang,

So I applied the v6 patch series to my 5.14-rc3 as it's what you
indicated is what v6 was based at, and injected a hardware poison.

I'm seeing the same problem that was reported a while ago after the
poison was consumed - in the SIGBUS payload, the si_addr is missing:

** SIGBUS(7): canjmp=1, whichstep=0, **
** si_addr(0x(nil)), si_lsb(0xC), si_code(0x4, BUS_MCEERR_AR) **

The si_addr ought to be 0x7f6568000000 - the vaddr of the first page
in this case.

The failure came from here :

[PATCH RESEND v6 6/9] xfs: Implement ->notify_failure() for XFS

+static int
+xfs_dax_notify_failure(
...
+    if (!xfs_sb_version_hasrmapbt(&mp->m_sb)) {
+        xfs_warn(mp, "notify_failure() needs rmapbt enabled!");
+        return -EOPNOTSUPP;
+    }

I am not familiar with XFS, but I have a few questions I hope to get
answers -

1) What does it take and cost to make
    xfs_sb_version_hasrmapbt(&mp->m_sb) to return true?

Enable rmpabt feature when making xfs filesystem
   `mkfs.xfs -m rmapbt=1 /path/to/device`
BTW, reflink is enabled by default.

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2) For a running environment that fails the above check, is it
    okay to leave the poison handle in limbo and why?

It will fall back to the old handler.  I think you have already known it.

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3) If the above regression is not acceptable, any potential remedy?

How about moving the check to prior to the notifier registration?
And register only if the check is passed?  This seems better than an
alternative which is to fall back to the legacy memory_failure handling in case
the filesystem returns -EOPNOTSUPP.

Sounds like a nice solution.  I think I can add an is_notify_supported() interface in dax_holder_ops and check it when register dax_holder.

--
Thanks,
Ruan.

thanks,
-jane

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thanks!
-jane

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Something is not right...

thanks,
-jane


On 8/5/2021 6:17 PM, Jane Chu wrote:

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The filesystem part of the pmem failure handling is at minimum built
on PAGE_SIZE granularity - an inheritance from general
memory_failure handling.  However, with Intel's DCPMEM technology,
the error blast radius is no more than 256bytes, and might get
smaller with future hardware generation, also advanced atomic 64B write

to clear the poison.

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But I don't see any of that could be incorporated in, given that the
filesystem is notified a corruption with pfn, rather than an exact
address.

So I guess this question is also for Dan: how to avoid unnecessarily
repairing a PMD range for a 256B corrupt range going forward?

thanks,
-jane


On 7/30/2021 3:01 AM, Shiyang Ruan wrote:

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When memory-failure occurs, we call this function which is
implemented by each kind of devices.  For the fsdax case, pmem
device driver implements it.  Pmem device driver will find out the
filesystem in which the corrupted page located in.  And finally
call filesystem handler to deal with this error.

The filesystem will try to recover the corrupted data if necessary.