The patch titled
Subject: dax: fix ENOMEM handling in grab_mapping_entry()
has been added to the -mm tree. Its filename is
dax-fix-enomem-handling-in-grab_mapping_entry.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/dax-fix-enomem-handling-in-grab_mapping_entry.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/dax-fix-enomem-handling-in-grab_mapping_entry.patch
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: 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@xxxxxxx
Fixes: b15cd800682f ("dax: Convert page fault handlers to XArray")
Signed-off-by: Jan Kara <jack@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/dax.c~dax-fix-enomem-handling-in-grab_mapping_entry
+++ a/fs/dax.c
@@ -488,10 +488,11 @@ static void *grab_mapping_entry(struct x
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);
_
Patches currently in -mm which might be from jack@xxxxxxx are
dax-fix-enomem-handling-in-grab_mapping_entry.patch
mm-fix-comments-mentioning-i_mutex.patch
