The patch titled
Subject: Revert "dax: fix race between simultaneous faults"
has been added to the -mm tree. Its filename is
revert-dax-fix-race-between-simultaneous-faults.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/revert-dax-fix-race-between-simultaneous-faults.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/revert-dax-fix-race-between-simultaneous-faults.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Subject: Revert "dax: fix race between simultaneous faults"
This reverts 843172978bb92 ("dax: fix race between simultaneous faults").
The following two locking commits in the DAX code:
commit 843172978bb9 ("dax: fix race between simultaneous faults")
commit 46c043ede471 ("mm: take i_mmap_lock in unmap_mapping_range() for DAX")
introduced a number of deadlocks and other issues, and need to be reverted
for the v4.3 kernel. The list of issues in DAX after these commits (some
newly introduced by the commits, some preexisting) can be found here:
https://lkml.org/lkml/2015/9/25/602 (Subject: "Re: [PATCH] dax: fix
deadlock in __dax_fault").
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 33 ++++++++++++++++-----------------
mm/memory.c | 11 +++--------
2 files changed, 19 insertions(+), 25 deletions(-)
diff -puN fs/dax.c~revert-dax-fix-race-between-simultaneous-faults fs/dax.c
--- a/fs/dax.c~revert-dax-fix-race-between-simultaneous-faults
+++ a/fs/dax.c
@@ -285,6 +285,7 @@ static int copy_user_bh(struct page *to,
static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
struct vm_area_struct *vma, struct vm_fault *vmf)
{
+ struct address_space *mapping = inode->i_mapping;
sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
unsigned long vaddr = (unsigned long)vmf->virtual_address;
void __pmem *addr;
@@ -292,6 +293,8 @@ static int dax_insert_mapping(struct ino
pgoff_t size;
int error;
+ i_mmap_lock_read(mapping);
+
/*
* Check truncate didn't happen while we were allocating a block.
* If it did, this block may or may not be still allocated to the
@@ -321,6 +324,8 @@ static int dax_insert_mapping(struct ino
error = vm_insert_mixed(vma, vaddr, pfn);
out:
+ i_mmap_unlock_read(mapping);
+
return error;
}
@@ -382,17 +387,15 @@ int __dax_fault(struct vm_area_struct *v
* from a read fault and we've raced with a truncate
*/
error = -EIO;
- goto unlock;
+ goto unlock_page;
}
- } else {
- i_mmap_lock_write(mapping);
}
error = get_block(inode, block, &bh, 0);
if (!error && (bh.b_size < PAGE_SIZE))
error = -EIO; /* fs corruption? */
if (error)
- goto unlock;
+ goto unlock_page;
if (!buffer_mapped(&bh) && !buffer_unwritten(&bh) && !vmf->cow_page) {
if (vmf->flags & FAULT_FLAG_WRITE) {
@@ -403,9 +406,8 @@ int __dax_fault(struct vm_area_struct *v
if (!error && (bh.b_size < PAGE_SIZE))
error = -EIO;
if (error)
- goto unlock;
+ goto unlock_page;
} else {
- i_mmap_unlock_write(mapping);
return dax_load_hole(mapping, page, vmf);
}
}
@@ -417,15 +419,17 @@ int __dax_fault(struct vm_area_struct *v
else
clear_user_highpage(new_page, vaddr);
if (error)
- goto unlock;
+ goto unlock_page;
vmf->page = page;
if (!page) {
+ i_mmap_lock_read(mapping);
/* Check we didn't race with truncate */
size = (i_size_read(inode) + PAGE_SIZE - 1) >>
PAGE_SHIFT;
if (vmf->pgoff >= size) {
+ i_mmap_unlock_read(mapping);
error = -EIO;
- goto unlock;
+ goto out;
}
}
return VM_FAULT_LOCKED;
@@ -461,8 +465,6 @@ int __dax_fault(struct vm_area_struct *v
WARN_ON_ONCE(!(vmf->flags & FAULT_FLAG_WRITE));
}
- if (!page)
- i_mmap_unlock_write(mapping);
out:
if (error == -ENOMEM)
return VM_FAULT_OOM | major;
@@ -471,14 +473,11 @@ int __dax_fault(struct vm_area_struct *v
return VM_FAULT_SIGBUS | major;
return VM_FAULT_NOPAGE | major;
- unlock:
+ unlock_page:
if (page) {
unlock_page(page);
page_cache_release(page);
- } else {
- i_mmap_unlock_write(mapping);
}
-
goto out;
}
EXPORT_SYMBOL(__dax_fault);
@@ -556,10 +555,10 @@ int __dax_pmd_fault(struct vm_area_struc
block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
bh.b_size = PMD_SIZE;
- i_mmap_lock_write(mapping);
length = get_block(inode, block, &bh, write);
if (length)
return VM_FAULT_SIGBUS;
+ i_mmap_lock_read(mapping);
/*
* If the filesystem isn't willing to tell us the length of a hole,
@@ -634,11 +633,11 @@ int __dax_pmd_fault(struct vm_area_struc
}
out:
+ i_mmap_unlock_read(mapping);
+
if (buffer_unwritten(&bh))
complete_unwritten(&bh, !(result & VM_FAULT_ERROR));
- i_mmap_unlock_write(mapping);
-
return result;
fallback:
diff -puN mm/memory.c~revert-dax-fix-race-between-simultaneous-faults mm/memory.c
--- a/mm/memory.c~revert-dax-fix-race-between-simultaneous-faults
+++ a/mm/memory.c
@@ -2427,16 +2427,11 @@ void unmap_mapping_range(struct address_
details.last_index = ULONG_MAX;
- /*
- * DAX already holds i_mmap_lock to serialise file truncate vs
- * page fault and page fault vs page fault.
- */
- if (!IS_DAX(mapping->host))
- i_mmap_lock_write(mapping);
+ /* DAX uses i_mmap_lock to serialise file truncate vs page fault */
+ i_mmap_lock_write(mapping);
if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap)))
unmap_mapping_range_tree(&mapping->i_mmap, &details);
- if (!IS_DAX(mapping->host))
- i_mmap_unlock_write(mapping);
+ i_mmap_unlock_write(mapping);
}
EXPORT_SYMBOL(unmap_mapping_range);
_
Patches currently in -mm which might be from ross.zwisler@xxxxxxxxxxxxxxx are
revert-mm-take-i_mmap_lock-in-unmap_mapping_range-for-dax.patch
revert-dax-fix-race-between-simultaneous-faults.patch
dax-temporarily-disable-dax-pmd-fault-path.patch
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