From: Jan Kara jack@suse.cz
[ Upstream commit 1a14e3779dd58c16b30e56558146e5cc850ba8b0 ]
grab_mapping_entry() has a bug in handling of ENOMEM condition. Suppose we have a PMD entry at index i which we are downgrading to a PTE entry. grab_mapping_entry() will set pmd_downgrade to true, lock the entry, clear the entry in xarray, and decrement mapping->nrpages. The it will call:
entry = dax_make_entry(pfn_to_pfn_t(0), flags); dax_lock_entry(xas, entry);
which inserts new PTE entry into xarray. However this may fail allocating the new node. We handle this by:
if (xas_nomem(xas, mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM)) goto retry;
however pmd_downgrade stays set to true even though 'entry' returned from get_unlocked_entry() will be NULL now. And we will go again through the downgrade branch. This is mostly harmless except that mapping->nrpages is decremented again and we temporarily have an invalid entry stored in xarray. Fix the problem by setting pmd_downgrade to false each time we lookup the entry we work with so that it matches the entry we found.
Link: https://lkml.kernel.org/r/20210622160015.18004-1-jack@suse.cz Fixes: b15cd800682f ("dax: Convert page fault handlers to XArray") Signed-off-by: Jan Kara jack@suse.cz Reviewed-by: Dan Williams dan.j.williams@intel.com Cc: Matthew Wilcox willy@infradead.org Cc: "Aneesh Kumar K.V" aneesh.kumar@linux.ibm.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/dax.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/dax.c b/fs/dax.c index 3b0e5da96d54..12953e892bb2 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -477,10 +477,11 @@ static void *grab_mapping_entry(struct xa_state *xas, struct address_space *mapping, unsigned int order) { unsigned long index = xas->xa_index; - bool pmd_downgrade = false; /* splitting PMD entry into PTE entries? */ + bool pmd_downgrade; /* splitting PMD entry into PTE entries? */ void *entry;
retry: + pmd_downgrade = false; xas_lock_irq(xas); entry = get_unlocked_entry(xas, order);