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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.

Fixes: 3a8e9ac89e ("writeback: add tracepoints for cgroup foreign writebacks")
Reported-by: Jan Kara <jack@suse.cz>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo 2019-08-30 16:39:54 -07:00 committed by Jens Axboe
parent 8f5914bcee
commit 0feacaa216
1 changed files with 4 additions and 1 deletions
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5
include/trace/events/writeback.h
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@ -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;