d6b473bae1
that was introduced in revision 1.80. The problem manifested
itself with a `locking against myself' panic and could also
result in soft updates inconsistences associated with inodedeps.
The two problems are:
1) One of the background operations could manipulate the bitmap
while holding it locked with intent to create. This held lock
results in a `locking against myself' panic, when the background
processing that we have been coopted to do tries to lock the bitmap
which we are already holding locked. To understand how to fix this
problem, first, observe that we can do the background cleanups in
inodedep_lookup only when allocating inodedeps (DEPALLOC is set in
the call to inodedep_lookup). Second observe that calls to
inodedep_lookup with DEPALLOC set can only happen from the following
calls into the softdep code:
softdep_setup_inomapdep
softdep_setup_allocdirect
softdep_setup_remove
softdep_setup_freeblocks
softdep_setup_directory_change
softdep_setup_directory_add
softdep_change_linkcnt
Only the first two of these can come from ffs_alloc.c while holding
a bitmap locked. Thus, inodedep_lookup must not go off to do
request_cleanups when being called from these functions. This change
adds a flag, NODELAY, that can be passed to inodedep_lookup to let
it know that it should not do background processing in those cases.
2) The return value from request_cleanup when helping out with the
cleanup was 0 instead of 1. This meant that despite the fact that
we may have slept while doing the cleanups, the code did not recheck
for the appearance of an inodedep (e.g., goto top in inodedep_lookup).
This lead to the softdep inconsistency in which we ended up with
two inodedep's for the same inode.
Reviewed by: Peter Wemm <peter@yahoo-inc.com>,
Matt Dillon <dillon@earth.backplane.com>
|
||
|---|---|---|
| .. | ||
| ffs_alloc.c | ||
| ffs_balloc.c | ||
| ffs_extern.h | ||
| ffs_inode.c | ||
| ffs_snapshot.c | ||
| ffs_softdep_stub.c | ||
| ffs_softdep.c | ||
| ffs_subr.c | ||
| ffs_tables.c | ||
| ffs_vfsops.c | ||
| ffs_vnops.c | ||
| fs.h | ||
| README.snapshot | ||
| README.softupdates | ||
| softdep.h | ||
$FreeBSD$ Using Soft Updates To enable the soft updates feature in your kernel, add option SOFTUPDATES to your kernel configuration. Once you are running a kernel with soft update support, you need to enable it for whichever filesystems you wish to run with the soft update policy. This is done with the -n option to tunefs(8) on the UNMOUNTED filesystems, e.g. from single-user mode you'd do something like: tunefs -n enable /usr To permanently enable soft updates on the /usr filesystem (or at least until a corresponding ``tunefs -n disable'' is done). Soft Updates Copyright Restrictions As of June 2000 the restrictive copyright has been removed and replaced with a `Berkeley-style' copyright. The files implementing soft updates now reside in the sys/ufs/ffs directory and are compiled into the generic kernel by default. Soft Updates Status The soft updates code has been running in production on many systems for the past two years generally quite successfully. The two current sets of shortcomings are: 1) On filesystems that are chronically full, the two minute lag from the time a file is deleted until its free space shows up will result in premature filesystem full failures. This failure mode is most evident in small filesystems such as the root. For this reason, use of soft updates is not recommended on the root filesystem. 2) If your system routines runs parallel processes each of which remove many files, the kernel memory rate limiting code may not be able to slow removal operations to a level sustainable by the disk subsystem. The result is that the kernel runs out of memory and hangs. Both of these problems are being addressed, but have not yet been resolved. There are no other known problems at this time. How Soft Updates Work For more general information on soft updates, please see: http://www.mckusick.com/softdep/ http://www.ece.cmu.edu/~ganger/papers/CSE-TR-254-95/ -- Marshall Kirk McKusick <mckusick@mckusick.com> July 2000