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author | Al Viro <viro@zeniv.linux.org.uk> | 2015-06-17 18:02:56 +0200 |
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committer | Al Viro <viro@zeniv.linux.org.uk> | 2015-07-06 23:39:25 +0200 |
commit | 724bb09fdc06d4ff03757b25d6dba9ef1b133e8f (patch) | |
tree | 5ef4441867f681e132d820c78948b34c0f0ca1df /fs/ufs/balloc.c | |
parent | ufs: bforget() indirect blocks before freeing them (diff) | |
download | linux-724bb09fdc06d4ff03757b25d6dba9ef1b133e8f.tar.xz linux-724bb09fdc06d4ff03757b25d6dba9ef1b133e8f.zip |
ufs: don't use lock_ufs() for block pointers tree protection
* stores to block pointers are under per-inode seqlock (meta_lock) and
mutex (truncate_mutex)
* fetches of block pointers are either under truncate_mutex, or wrapped
into seqretry loop on meta_lock
* all changes of ->i_size are under truncate_mutex and i_mutex
* all changes of ->i_lastfrag are under truncate_mutex
It's similar to what ext2 is doing; the main difference is that unlike
ext2 we can't rely upon the atomicity of stores into block pointers -
on UFS2 they are 64bit. So we can't cut the corner when switching
a pointer from NULL to non-NULL as we could in ext2_splice_branch()
and need to use meta_lock on all modifications.
We use seqlock where ext2 uses rwlock; ext2 could probably also benefit
from such change...
Another non-trivial difference is that with UFS we *cannot* have reader
grab truncate_mutex in case of race - it has to keep retrying. That
might be possible to change, but not until we lift tail unpacking
several levels up in call chain.
After that commit we do *NOT* hold fs-wide serialization on accesses
to block pointers anymore. Moreover, lock_ufs() can become a normal
mutex now - it's only used on statfs, remount and sync_fs and none
of those uses are recursive. As the matter of fact, *now* it can be
collapsed with ->s_lock, and be eventually replaced with saner
per-cylinder-group spinlocks, but that's a separate story.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/ufs/balloc.c')
-rw-r--r-- | fs/ufs/balloc.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/fs/ufs/balloc.c b/fs/ufs/balloc.c index a7106eda5024..fb8b54eb77c5 100644 --- a/fs/ufs/balloc.c +++ b/fs/ufs/balloc.c @@ -417,7 +417,9 @@ u64 ufs_new_fragments(struct inode *inode, void *p, u64 fragment, if (oldcount == 0) { result = ufs_alloc_fragments (inode, cgno, goal, count, err); if (result) { + write_seqlock(&UFS_I(inode)->meta_lock); ufs_cpu_to_data_ptr(sb, p, result); + write_sequnlock(&UFS_I(inode)->meta_lock); *err = 0; UFS_I(inode)->i_lastfrag = max(UFS_I(inode)->i_lastfrag, fragment + count); @@ -473,7 +475,9 @@ u64 ufs_new_fragments(struct inode *inode, void *p, u64 fragment, ufs_change_blocknr(inode, fragment - oldcount, oldcount, uspi->s_sbbase + tmp, uspi->s_sbbase + result, locked_page); + write_seqlock(&UFS_I(inode)->meta_lock); ufs_cpu_to_data_ptr(sb, p, result); + write_sequnlock(&UFS_I(inode)->meta_lock); *err = 0; UFS_I(inode)->i_lastfrag = max(UFS_I(inode)->i_lastfrag, fragment + count); |