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authorJan Kara <jack@suse.cz>2021-06-28 19:35:04 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-06-29 10:53:47 -0700
commit1a14e3779dd58c16b30e56558146e5cc850ba8b0 (patch)
treeaf8f0b00634072f42e1b1c944d81be0bd8cf8929 /fs
parent54dd200c5a251b5db9f6f0f72a251c28e0d7da43 (diff)
dax: fix ENOMEM handling in grab_mapping_entry()
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>
Diffstat (limited to 'fs')
-rw-r--r--fs/dax.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/fs/dax.c b/fs/dax.c
index 62352cbcf0f4..da41f9363568 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -488,10 +488,11 @@ 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);