From: Jan Kara <jack@suse.cz>
To: Jeff Layton <jlayton@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org,
linux-mm@kvack.org, jfs-discussion@lists.sourceforge.net,
linux-xfs@vger.kernel.org, cluster-devel@redhat.com,
linux-f2fs-devel@lists.sourceforge.net,
v9fs-developer@lists.sourceforge.net,
linux-nilfs@vger.kernel.org, linux-block@vger.kernel.org,
dhowells@redhat.com, akpm@linux-foundation.org,
hch@infradead.org, ross.zwisler@linux.intel.com,
mawilcox@microsoft.com, jack@suse.com, viro@zeniv.linux.org.uk,
corbet@lwn.net, neilb@suse.de, clm@fb.com, tytso@mit.edu,
axboe@kernel.dk, josef@toxicpanda.com, hubcap@omnibond.com,
rpeterso@redhat.com, bo.li.liu@oracle.com
Subject: Re: [PATCH v4 13/27] lib: add errseq_t type and infrastructure for handling it
Date: Wed, 10 May 2017 13:34:30 +0200 [thread overview]
Message-ID: <20170510113430.GE25137@quack2.suse.cz> (raw)
In-Reply-To: <20170509154930.29524-14-jlayton@redhat.com>
On Tue 09-05-17 11:49:16, Jeff Layton wrote:
> An errseq_t is a way of recording errors in one place, and allowing any
> number of "subscribers" to tell whether an error has been set again
> since a previous time.
>
> It's implemented as an unsigned 32-bit value that is managed with atomic
> operations. The low order bits are designated to hold an error code
> (max size of MAX_ERRNO). The upper bits are used as a counter.
>
> The API works with consumers sampling an errseq_t value at a particular
> point in time. Later, that value can be used to tell whether new errors
> have been set since that time.
>
> Note that there is a 1 in 512k risk of collisions here if new errors
> are being recorded frequently, since we have so few bits to use as a
> counter. To mitigate this, one bit is used as a flag to tell whether the
> value has been sampled since a new value was recorded. That allows
> us to avoid bumping the counter if no one has sampled it since it
> was last bumped.
>
> Later patches will build on this infrastructure to change how writeback
> errors are tracked in the kernel.
>
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
The patch looks good to me. Feel free to add:
Reviewed-by: Jan Kara <jack@suse.cz>
Just two nits below:
...
> +int errseq_check_and_advance(errseq_t *eseq, errseq_t *since)
> +{
> + int err = 0;
> + errseq_t old, new;
> +
> + /*
> + * Most callers will want to use the inline wrapper to check this,
> + * so that the common case of no error is handled without needing
> + * to lock.
> + */
I'm not sure which locking you are speaking about here. Is the comment
stale?
> + old = READ_ONCE(*eseq);
> + if (old != *since) {
> + /*
> + * Set the flag and try to swap it into place if it has
> + * changed.
> + *
> + * We don't care about the outcome of the swap here. If the
> + * swap doesn't occur, then it has either been updated by a
> + * writer who is bumping the seq count anyway, or another
"bumping the seq count anyway" part is not quite true. Writer may see
ERRSEQ_SEEN not set and so just update the error code and leave seq count
as is. But since you compare full errseq_t for equality, this works out as
designed...
> + * reader who is just setting the "seen" flag. Either outcome
> + * is OK, and we can advance "since" and return an error based
> + * on what we have.
> + */
> + new = old | ERRSEQ_SEEN;
> + if (new != old)
> + cmpxchg(eseq, old, new);
> + *since = new;
> + err = -(new & MAX_ERRNO);
> + }
> + return err;
> +}
> +EXPORT_SYMBOL(errseq_check_and_advance);
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2017-05-10 11:34 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-09 15:49 [PATCH v4 00/27] fs: introduce new writeback error reporting and convert existing API as a wrapper around it Jeff Layton
2017-05-09 15:49 ` [PATCH v4 01/27] fs: remove unneeded forward definition of mm_struct from fs.h Jeff Layton
2017-05-10 11:04 ` Jan Kara
2017-05-09 15:49 ` [PATCH v4 02/27] mm: drop "wait" parameter from write_one_page Jeff Layton
2017-05-09 15:49 ` [PATCH v4 03/27] mm: fix mapping_set_error call in me_pagecache_dirty Jeff Layton
2017-05-09 15:49 ` [PATCH v4 04/27] buffer: use mapping_set_error instead of setting the flag Jeff Layton
2017-05-09 15:49 ` [PATCH v4 05/27] btrfs: btrfs_wait_tree_block_writeback can be void return Jeff Layton
2017-05-10 11:09 ` Jan Kara
2017-05-19 4:07 ` Liu Bo
2017-05-09 15:49 ` [PATCH v4 06/27] fs: check for writeback errors after syncing out buffers in generic_file_fsync Jeff Layton
2017-05-10 12:48 ` Matthew Wilcox
2017-05-09 15:49 ` [PATCH v4 07/27] orangefs: don't call filemap_write_and_wait from fsync Jeff Layton
2017-05-09 15:49 ` [PATCH v4 08/27] dax: set errors in mapping when writeback fails Jeff Layton
2017-05-09 15:49 ` [PATCH v4 09/27] nilfs2: set the mapping error when calling SetPageError on writeback Jeff Layton
2017-05-09 15:49 ` [PATCH v4 10/27] 9p: set mapping error when writeback fails in launder_page Jeff Layton
2017-05-09 15:49 ` [PATCH v4 11/27] fuse: set mapping error in writepage_locked when it fails Jeff Layton
2017-05-10 11:13 ` Jan Kara
2017-05-09 15:49 ` [PATCH v4 12/27] cifs: set mapping error when page writeback fails in writepage or launder_pages Jeff Layton
2017-05-10 11:14 ` Jan Kara
2017-05-09 15:49 ` [PATCH v4 13/27] lib: add errseq_t type and infrastructure for handling it Jeff Layton
2017-05-09 22:03 ` NeilBrown
2017-05-10 11:29 ` Jeff Layton
2017-05-10 11:34 ` Jan Kara [this message]
2017-05-10 11:58 ` Jeff Layton
2017-05-10 14:18 ` Matthew Wilcox
2017-05-10 14:56 ` Jeff Layton
2017-05-09 15:49 ` [PATCH v4 14/27] fs: new infrastructure for writeback error handling and reporting Jeff Layton
2017-05-10 11:48 ` Jan Kara
2017-05-10 12:19 ` Jeff Layton
2017-05-10 13:46 ` Jan Kara
2017-05-09 15:49 ` [PATCH v4 15/27] fs: retrofit old error reporting API onto new infrastructure Jeff Layton
2017-05-15 10:42 ` Jan Kara
2017-05-15 17:58 ` Jeff Layton
2017-05-19 19:20 ` Jeff Layton
2017-05-22 13:38 ` Jan Kara
2017-05-22 13:53 ` Jeff Layton
2017-05-22 17:53 ` Jan Kara
2017-05-22 19:09 ` Jeff Layton
2017-05-23 9:05 ` Jan Kara
2017-05-09 15:49 ` [PATCH v4 16/27] fs: adapt sync_file_range to new reporting infrastructure Jeff Layton
2017-05-09 15:49 ` [PATCH v4 17/27] mm: remove AS_EIO and AS_ENOSPC flags Jeff Layton
2017-05-09 15:49 ` [PATCH v4 18/27] mm: don't TestClearPageError in __filemap_fdatawait_range Jeff Layton
2017-05-09 15:49 ` [PATCH v4 19/27] buffer: set errors in mapping at the time that the error occurs Jeff Layton
2017-05-15 11:53 ` Jan Kara
2017-05-09 15:49 ` [PATCH v4 20/27] cifs: cleanup writeback handling errors and comments Jeff Layton
2017-05-09 15:49 ` [PATCH v4 21/27] mm: clean up error handling in write_one_page Jeff Layton
2017-05-15 12:01 ` Jan Kara
2017-05-09 15:49 ` [PATCH v4 22/27] jbd2: don't reset error in journal_finish_inode_data_buffers Jeff Layton
2017-05-15 11:58 ` Jan Kara
2017-05-09 15:49 ` [PATCH v4 23/27] gfs2: clean up some filemap_* calls Jeff Layton
2017-05-10 16:18 ` Bob Peterson
2017-05-09 15:49 ` [PATCH v4 24/27][RFC] nfs: convert to new errseq_t based error tracking for writeback errors Jeff Layton
2017-05-09 15:49 ` [PATCH v4 25/27] Documentation: flesh out the section in vfs.txt on storing and reporting " Jeff Layton
2017-05-09 16:24 ` Jeff Layton
2017-05-09 15:49 ` [PATCH v4 26/27] mm: flesh out comments over mapping_set_error Jeff Layton
2017-05-09 15:49 ` [PATCH v4 27/27] mm: clean up comments in me_pagecache_dirty Jeff Layton
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