DAX will return to locking exceptional entry before mapping blocks
for a page fault to fix possible races with concurrent writes. To avoid
lock inversion between exceptional entry lock and transaction start,
start the transaction already in ext4_dax_huge_fault().
Fixes: 9f141d6ef6258a3a37a045842d9ba7e68f368956
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/ext4/file.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index cefa9835f275..831fd6beebf0 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -257,6 +257,7 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf,
enum page_entry_size pe_size)
{
int result;
+ handle_t *handle = NULL;
struct inode *inode = file_inode(vmf->vma->vm_file);
struct super_block *sb = inode->i_sb;
bool write = vmf->flags & FAULT_FLAG_WRITE;
@@ -264,12 +265,24 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf,
if (write) {
sb_start_pagefault(sb);
file_update_time(vmf->vma->vm_file);
+ down_read(&EXT4_I(inode)->i_mmap_sem);
+ handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE,
+ EXT4_DATA_TRANS_BLOCKS(sb));
+ } else {
+ down_read(&EXT4_I(inode)->i_mmap_sem);
}
- down_read(&EXT4_I(inode)->i_mmap_sem);
- result = dax_iomap_fault(vmf, pe_size, &ext4_iomap_ops);
- up_read(&EXT4_I(inode)->i_mmap_sem);
- if (write)
+ if (!IS_ERR(handle))
+ result = dax_iomap_fault(vmf, pe_size, &ext4_iomap_ops);
+ else
+ result = VM_FAULT_SIGBUS;
+ if (write) {
+ if (!IS_ERR(handle))
+ ext4_journal_stop(handle);
+ up_read(&EXT4_I(inode)->i_mmap_sem);
sb_end_pagefault(sb);
+ } else {
+ up_read(&EXT4_I(inode)->i_mmap_sem);
+ }
return result;
}
--
2.12.0
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