The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From c93db7bb6ef3251e0ea48ade311d3e9942748e1c Mon Sep 17 00:00:00 2001
From: Matthew Wilcox willy@infradead.org Date: Tue, 27 Nov 2018 13:16:33 -0800 Subject: [PATCH] dax: Check page->mapping isn't NULL
If we race with inode destroy, it's possible for page->mapping to be NULL before we even enter this routine, as well as after having slept waiting for the dax entry to become unlocked.
Fixes: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()") Cc: stable@vger.kernel.org Reported-by: Jan Kara jack@suse.cz Signed-off-by: Matthew Wilcox willy@infradead.org Reviewed-by: Johannes Thumshirn jthumshirn@suse.de Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Dan Williams dan.j.williams@intel.com
diff --git a/fs/dax.c b/fs/dax.c index 9bcce89ea18e..e69fc231833b 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -365,7 +365,7 @@ bool dax_lock_mapping_entry(struct page *page) struct address_space *mapping = READ_ONCE(page->mapping);
locked = false; - if (!dax_mapping(mapping)) + if (!mapping || !dax_mapping(mapping)) break;
/*