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Message-ID: <20151014085119.GB23758@quack.suse.cz>
Date: Wed, 14 Oct 2015 10:51:19 +0200
From: Jan Kara <jack@...e.cz>
To: Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org,
Alexander Viro <viro@...iv.linux.org.uk>,
Jan Kara <jack@...e.com>,
Matthew Wilcox <willy@...ux.intel.com>,
linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Dan Williams <dan.j.williams@...el.com>,
Dave Chinner <david@...morbit.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
linux-nvdimm@...ts.01.org,
Matthew Wilcox <matthew.r.wilcox@...el.com>
Subject: Re: [PATCH v2 2/2] ext2: Add locking for DAX faults
On Tue 13-10-15 16:25:37, Ross Zwisler wrote:
> Add locking to ensure that DAX faults are isolated from ext2 operations
> that modify the data blocks allocation for an inode. This is intended to
> be analogous to the work being done in XFS by Dave Chinner:
>
> http://www.spinics.net/lists/linux-fsdevel/msg90260.html
>
> Compared with XFS the ext2 case is greatly simplified by the fact that ext2
> already allocates and zeros new blocks before they are returned as part of
> ext2_get_block(), so DAX doesn't need to worry about getting unmapped or
> unwritten buffer heads.
>
> This means that the only work we need to do in ext2 is to isolate the DAX
> faults from inode block allocation changes. I believe this just means that
> we need to isolate the DAX faults from truncate operations.
>
> The newly introduced dax_sem is intended to replicate the protection
> offered by i_mmaplock in XFS. In addition to truncate the i_mmaplock also
> protects XFS operations like hole punching, fallocate down, extent
> manipulation IOCTLS like xfs_ioc_space() and extent swapping. Truncate is
> the only one of these operations supported by ext2.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
The patch looks good to me. Feel free to add:
Reviewed-by: Jan Kara <jack@...e.com>
Or I can push the patch through my tree as it seems to be independent of
any other changes, am I right?
Honza
> ---
> fs/ext2/ext2.h | 11 ++++++++
> fs/ext2/file.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
> fs/ext2/inode.c | 10 +++++++
> fs/ext2/super.c | 3 +++
> 4 files changed, 104 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ext2/ext2.h b/fs/ext2/ext2.h
> index 8d15feb..4c69c94 100644
> --- a/fs/ext2/ext2.h
> +++ b/fs/ext2/ext2.h
> @@ -684,6 +684,9 @@ struct ext2_inode_info {
> struct rw_semaphore xattr_sem;
> #endif
> rwlock_t i_meta_lock;
> +#ifdef CONFIG_FS_DAX
> + struct rw_semaphore dax_sem;
> +#endif
>
> /*
> * truncate_mutex is for serialising ext2_truncate() against
> @@ -699,6 +702,14 @@ struct ext2_inode_info {
> #endif
> };
>
> +#ifdef CONFIG_FS_DAX
> +#define dax_sem_down_write(ext2_inode) down_write(&(ext2_inode)->dax_sem)
> +#define dax_sem_up_write(ext2_inode) up_write(&(ext2_inode)->dax_sem)
> +#else
> +#define dax_sem_down_write(ext2_inode)
> +#define dax_sem_up_write(ext2_inode)
> +#endif
> +
> /*
> * Inode dynamic state flags
> */
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index 1982c3f..11a42c5 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -27,27 +27,103 @@
> #include "acl.h"
>
> #ifdef CONFIG_FS_DAX
> +/*
> + * The lock ordering for ext2 DAX fault paths is:
> + *
> + * mmap_sem (MM)
> + * sb_start_pagefault (vfs, freeze)
> + * ext2_inode_info->dax_sem
> + * address_space->i_mmap_rwsem or page_lock (mutually exclusive in DAX)
> + * ext2_inode_info->truncate_mutex
> + *
> + * The default page_lock and i_size verification done by non-DAX fault paths
> + * is sufficient because ext2 doesn't support hole punching.
> + */
> static int ext2_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> {
> - return dax_fault(vma, vmf, ext2_get_block, NULL);
> + struct inode *inode = file_inode(vma->vm_file);
> + struct ext2_inode_info *ei = EXT2_I(inode);
> + int ret;
> +
> + if (vmf->flags & FAULT_FLAG_WRITE) {
> + sb_start_pagefault(inode->i_sb);
> + file_update_time(vma->vm_file);
> + }
> + down_read(&ei->dax_sem);
> +
> + ret = __dax_fault(vma, vmf, ext2_get_block, NULL);
> +
> + up_read(&ei->dax_sem);
> + if (vmf->flags & FAULT_FLAG_WRITE)
> + sb_end_pagefault(inode->i_sb);
> + return ret;
> }
>
> static int ext2_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
> pmd_t *pmd, unsigned int flags)
> {
> - return dax_pmd_fault(vma, addr, pmd, flags, ext2_get_block, NULL);
> + struct inode *inode = file_inode(vma->vm_file);
> + struct ext2_inode_info *ei = EXT2_I(inode);
> + int ret;
> +
> + if (flags & FAULT_FLAG_WRITE) {
> + sb_start_pagefault(inode->i_sb);
> + file_update_time(vma->vm_file);
> + }
> + down_read(&ei->dax_sem);
> +
> + ret = __dax_pmd_fault(vma, addr, pmd, flags, ext2_get_block, NULL);
> +
> + up_read(&ei->dax_sem);
> + if (flags & FAULT_FLAG_WRITE)
> + sb_end_pagefault(inode->i_sb);
> + return ret;
> }
>
> static int ext2_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> {
> - return dax_mkwrite(vma, vmf, ext2_get_block, NULL);
> + struct inode *inode = file_inode(vma->vm_file);
> + struct ext2_inode_info *ei = EXT2_I(inode);
> + int ret;
> +
> + sb_start_pagefault(inode->i_sb);
> + file_update_time(vma->vm_file);
> + down_read(&ei->dax_sem);
> +
> + ret = __dax_mkwrite(vma, vmf, ext2_get_block, NULL);
> +
> + up_read(&ei->dax_sem);
> + sb_end_pagefault(inode->i_sb);
> + return ret;
> +}
> +
> +static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
> + struct vm_fault *vmf)
> +{
> + struct inode *inode = file_inode(vma->vm_file);
> + struct ext2_inode_info *ei = EXT2_I(inode);
> + int ret = VM_FAULT_NOPAGE;
> + loff_t size;
> +
> + sb_start_pagefault(inode->i_sb);
> + file_update_time(vma->vm_file);
> + down_read(&ei->dax_sem);
> +
> + /* check that the faulting page hasn't raced with truncate */
> + size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
> + if (vmf->pgoff >= size)
> + ret = VM_FAULT_SIGBUS;
> +
> + up_read(&ei->dax_sem);
> + sb_end_pagefault(inode->i_sb);
> + return ret;
> }
>
> static const struct vm_operations_struct ext2_dax_vm_ops = {
> .fault = ext2_dax_fault,
> .pmd_fault = ext2_dax_pmd_fault,
> .page_mkwrite = ext2_dax_mkwrite,
> - .pfn_mkwrite = dax_pfn_mkwrite,
> + .pfn_mkwrite = ext2_dax_pfn_mkwrite,
> };
>
> static int ext2_file_mmap(struct file *file, struct vm_area_struct *vma)
> diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> index c60a248..0aa9bf6 100644
> --- a/fs/ext2/inode.c
> +++ b/fs/ext2/inode.c
> @@ -1085,6 +1085,7 @@ static void ext2_free_branches(struct inode *inode, __le32 *p, __le32 *q, int de
> ext2_free_data(inode, p, q);
> }
>
> +/* dax_sem must be held when calling this function */
> static void __ext2_truncate_blocks(struct inode *inode, loff_t offset)
> {
> __le32 *i_data = EXT2_I(inode)->i_data;
> @@ -1100,6 +1101,10 @@ static void __ext2_truncate_blocks(struct inode *inode, loff_t offset)
> blocksize = inode->i_sb->s_blocksize;
> iblock = (offset + blocksize-1) >> EXT2_BLOCK_SIZE_BITS(inode->i_sb);
>
> +#ifdef CONFIG_FS_DAX
> + WARN_ON(!rwsem_is_locked(&ei->dax_sem));
> +#endif
> +
> n = ext2_block_to_path(inode, iblock, offsets, NULL);
> if (n == 0)
> return;
> @@ -1185,7 +1190,10 @@ static void ext2_truncate_blocks(struct inode *inode, loff_t offset)
> return;
> if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
> return;
> +
> + dax_sem_down_write(EXT2_I(inode));
> __ext2_truncate_blocks(inode, offset);
> + dax_sem_up_write(EXT2_I(inode));
> }
>
> static int ext2_setsize(struct inode *inode, loff_t newsize)
> @@ -1213,8 +1221,10 @@ static int ext2_setsize(struct inode *inode, loff_t newsize)
> if (error)
> return error;
>
> + dax_sem_down_write(EXT2_I(inode));
> truncate_setsize(inode, newsize);
> __ext2_truncate_blocks(inode, newsize);
> + dax_sem_up_write(EXT2_I(inode));
>
> inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
> if (inode_needs_sync(inode)) {
> diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> index 900e19c..3a71cea 100644
> --- a/fs/ext2/super.c
> +++ b/fs/ext2/super.c
> @@ -192,6 +192,9 @@ static void init_once(void *foo)
> init_rwsem(&ei->xattr_sem);
> #endif
> mutex_init(&ei->truncate_mutex);
> +#ifdef CONFIG_FS_DAX
> + init_rwsem(&ei->dax_sem);
> +#endif
> inode_init_once(&ei->vfs_inode);
> }
>
> --
> 2.1.0
>
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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