On Wed, 29 Sep 2010 22:18:39 +1000 Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> From: Nick Piggin <npiggin@xxxxxxx>
>
> The inode use statistics are currently protected by the inode_lock.
> Before we can remove the inode_lock, we need to protect these
> counters against races. Do this by converting them to atomic
> counters so they ar enot dependent on any lock at all.
typo
>
> ...
>
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -764,7 +764,8 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
> wb->last_old_flush = jiffies;
> nr_pages = global_page_state(NR_FILE_DIRTY) +
> global_page_state(NR_UNSTABLE_NFS) +
> - (inodes_stat.nr_inodes - inodes_stat.nr_unused);
> + (atomic_read(&inodes_stat.nr_inodes) -
> + atomic_read(&inodes_stat.nr_unused));
race bug.
> if (nr_pages) {
> struct wb_writeback_work work = {
> @@ -1144,7 +1145,8 @@ void writeback_inodes_sb(struct super_block *sb)
> WARN_ON(!rwsem_is_locked(&sb->s_umount));
>
> work.nr_pages = nr_dirty + nr_unstable +
> - (inodes_stat.nr_inodes - inodes_stat.nr_unused);
> + (atomic_read(&inodes_stat.nr_inodes) -
> + atomic_read(&inodes_stat.nr_unused));
and another.
OK, they aren't serious ones. But known regressions shouldn't be snuck
into the kernel unchangelogged and uncommented :(
> bdi_queue_work(sb->s_bdi, &work);
> wait_for_completion(&done);
>
> ...
>
> -struct inodes_stat_t {
> - int nr_inodes;
> - int nr_unused;
> - int dummy[5]; /* padding for sysctl ABI compatibility */
> -};
> -
> -
> #define NR_FILE 8192 /* this can well be larger on a larger system */
>
> #define MAY_EXEC 1
> @@ -416,6 +409,12 @@ typedef void (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
> ssize_t bytes, void *private, int ret,
> bool is_async);
>
> +struct inodes_stat_t {
> + atomic_t nr_inodes;
> + atomic_t nr_unused;
> + int dummy[5]; /* padding for sysctl ABI compatibility */
> +};
OK, that's a hack. The first two "ints" are copied out to userspace.
This change assumes that sizeof(atomic_t)=4 and that an atomic_t has
the same layout, alignment and padding as an int.
Probably that's true in current kernels and with current architectures
but it's a hack and it's presumptive.
It shouldn't be snuck into the tree unchangelogged and uncommented.
(time passes)
OK, I see that all of this gets reverted later on. Please update the
changelog so the next reviewer doesn't get fooled.
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