2019-08-30 23:41:02

by Tejun Heo

Subject: [block/for-next] writeback: don't access page->mapping directly in track_foreign_dirty TP

page->mapping may encode different values in it and page_mapping()
should always be used to access the mapping pointer.
track_foreign_dirty tracepoint was incorrectly accessing page->mapping
directly. Use page_mapping() instead. Also, add NULL checks while at
it.

Signed-off-by: Tejun Heo <[email protected]>
Reported-by: Jan Kara <[email protected]>
Fixes: 3a8e9ac89e6a ("writeback: add tracepoints for cgroup foreign writebacks")
---
include/trace/events/writeback.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 3dc9fb9e7c78..3a27335fce2c 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -251,9 +251,12 @@ TRACE_EVENT(track_foreign_dirty,
),

TP_fast_assign(
+ struct address_space *mapping = page_mapping(page);
+ struct inode *inode = mapping ? mapping->host : NULL;
+
strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
__entry->bdi_id = wb->bdi->id;
- __entry->ino = page->mapping->host->i_ino;
+ __entry->ino = inode ? inode->i_ino : 0;
__entry->memcg_id = wb->memcg_css->id;
__entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
__entry->page_cgroup_ino = page->mem_cgroup->css.cgroup->kn->id.ino;

2019-08-31 01:55:58

by Jens Axboe

Subject: Re: [block/for-next] writeback: don't access page->mapping directly in track_foreign_dirty TP

On 8/30/19 5:39 PM, Tejun Heo wrote:
> page->mapping may encode different values in it and page_mapping()
> should always be used to access the mapping pointer.
> track_foreign_dirty tracepoint was incorrectly accessing page->mapping
> directly. Use page_mapping() instead. Also, add NULL checks while at
> it.

Applied, thanks.

--
Jens Axboe

2019-09-02 09:43:37

by Jan Kara

Subject: Re: [block/for-next] writeback: don't access page->mapping directly in track_foreign_dirty TP

On Fri 30-08-19 16:39:54, Tejun Heo wrote:
> page->mapping may encode different values in it and page_mapping()
> should always be used to access the mapping pointer.
> track_foreign_dirty tracepoint was incorrectly accessing page->mapping
> directly. Use page_mapping() instead. Also, add NULL checks while at
> it.
>
> Signed-off-by: Tejun Heo <[email protected]>
> Reported-by: Jan Kara <[email protected]>
> Fixes: 3a8e9ac89e6a ("writeback: add tracepoints for cgroup foreign writebacks")

I can see Jens already picked this up so this is just informative: The patch
now looks good to me.

Honza

> ---
> include/trace/events/writeback.h | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
> index 3dc9fb9e7c78..3a27335fce2c 100644
> --- a/include/trace/events/writeback.h
> +++ b/include/trace/events/writeback.h
> @@ -251,9 +251,12 @@ TRACE_EVENT(track_foreign_dirty,
> ),
>
> TP_fast_assign(
> + struct address_space *mapping = page_mapping(page);
> + struct inode *inode = mapping ? mapping->host : NULL;
> +
> strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
> __entry->bdi_id = wb->bdi->id;
> - __entry->ino = page->mapping->host->i_ino;
> + __entry->ino = inode ? inode->i_ino : 0;
> __entry->memcg_id = wb->memcg_css->id;
> __entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
> __entry->page_cgroup_ino = page->mem_cgroup->css.cgroup->kn->id.ino;
--
Jan Kara <[email protected]>
SUSE Labs, CR