Re: vm page panic

[Kirk McKusick]

Date: Sun, 25 Mar 2001 11:20:17 +0200
From: Jeroen Ruigrok/Asmodai [EMAIL PROTECTED]
To: Kirk McKusick [EMAIL PROTECTED],
   Peter Wemm [EMAIL PROTECTED],
   Paul Saab [EMAIL PROTECTED], Matt Dillon [EMAIL PROTECTED],
   Soeren Schmidt [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]
Subject: vm page panic

Hi guys,

ok, sources cvsupped yesterday afternoon, just before my ffs_alloc.c
commit [which I did, obviously, add myself locally].

Box had been running for a while when all of a sudden it got into a
panic:

vm_page_alloc: free/cache page 0xc0776fa4 was dirty

a trace in ddb shows:

allocbuf()
getblk()
ffs_balloc()
ffs_write()
vn_rdwr()
elf_coredump()
coredump()

Unfortunately my ata controller didn't get reprobed [just was hanging
there] so I couldn't get a crashdump. =( [HPT366]

So consider this a heads-up, since you might encounter this.

Extra info:

devfs running,
/ is normal FFS
/tmp, /var, /usr, /storage all soft-updated.

-- 
Jeroen Ruigrok van der Werven/Asmodai .oUo. asmodai@[wxs.nl|freebsd.org]
Documentation nutter/C-rated Coder BSD: Technical excellence at its best  
  D78D D0AD 244D 1D12 C9CA  7152 035C 1138 546A B867
Pleasure's a sin, and sometimes sin's a pleasure...

The latest round of changes to ffs_alloc.c add code which is only ever
used by background fsck which is not yetbeing used. So, it seems
very unlikely that your panic has been triggered byv these changes.

Kirk

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Re: vm page panic

[Matt Dillon]

:   Hi guys,
:
:   ok, sources cvsupped yesterday afternoon, just before my ffs_alloc.c
:   commit [which I did, obviously, add myself locally].
:
:   Box had been running for a while when all of a sudden it got into a
:   panic:
:
:   vm_page_alloc: free/cache page 0xc0776fa4 was dirty
:
:   a trace in ddb shows:
:
:   allocbuf()
:   getblk()
:   ffs_balloc()
:   ffs_write()
:   vn_rdwr()
:   elf_coredump()
:   coredump()

This particular panic will have a delayed effect, so the trace probably
isn't the problem.  Something occured some period of time prior that
caused a (probably cache) page to be marked dirty.  Then later when
vm_page_alloc() tries to reuse the page it notices that it's dirty when
it shouldn't be.

I have not seen this panic literaly for years - there was a bug in 
John Dyson's original code that could cause it but it was fixed a very
long time ago.  So I'm guessing that the panic is a side effect of a
newly introduced bug somewhere in current.  Possibly a race of some sort
with the mutex/threading/interrupt code, but I don't know.

-Matt

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