cvs commit: src/sys/kern kern_shutdown.c
ups at tree.com
Wed Jul 21 13:45:22 PDT 2004
Alfred Perlstein wrote:
> * Scott Long <scottl at freebsd.org> [040721 09:57] wrote:
> > It should be noted that syncing on panic is almost never a good idea.
> > The whole idea of panic() is to signal that the system has gotten into
> > an inconsistent and unrecoverable state. Do you really want to trust it
> > to spam your drive with buffers that are in an unknown state via a set
> > of codepaths that are in an unknown state? It's much better to just
> > step back and let fsck try to repair the damage. I can't remember a
> > single time in the last 4 years when a panic actually successfuly synced
> > out all of the buffers and shutdown the filesystem, so it's not likely
> > that you'll avoid a fsck on reboot with this.
> It's not about avoiding a fsck, it's about recovering the last 30+ seconds
> of disk activity. Ie, files you've just created and such.
Locking is disabled during a sync on panic.
( all lockmgr requests succeed)
Even if the internal file system state is not corrupted
in a panic, multiple threads might be active in the filessystem
using locks to carefully update buffers or enforce the buffer
A sync requests trampling through the file systems with
total disregard for any locks can do interesting things
to a filesystem on disk.
I think adding a "dangerous" warning to the sysctl description
might be useful.
Otherwise it is hard to guess that by trying to save 30 seconds of
data one risks loosing the whole file system.
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