Re: [PATCH] mm: prevent concurrent unmap_mapping_range() on thesame inode

From: Hugh Dickins
Date: Wed Feb 23 2011 - 17:20:28 EST

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On Wed, 23 Feb 2011, Miklos Szeredi wrote:

> Linus, Andrew,
>
> This resolves Bug 25822 listed in the regressions since 2.6.36 (though
> it's a bug much older than that, for some reason it only started
> triggering for people recently).
>
> Summary of discussion of below patch by Hugh:
>
> An executive summary of the thread that followed would be that hch
> dislikes the bloat, as we all do, but Miklos and I don't see a
> decent alternative (and hch has not proposed one).
>
> Please consider this for 2.6.38.
>
> Thanks,
> Miklos
>
> ----
> Subject: mm: prevent concurrent unmap_mapping_range() on the same inode
>
> From: Miklos Szeredi <mszeredi@xxxxxxx>
>
> Michael Leun reported that running parallel opens on a fuse filesystem
> can trigger a "kernel BUG at mm/truncate.c:475"
>
> Gurudas Pai reported the same bug on NFS.
>
> The reason is, unmap_mapping_range() is not prepared for more than
> one concurrent invocation per inode. For example:

Yes, at the time I did that preemptible restart stuff 6 years ago,
i_mutex was always held by callers of unmap_mapping_range(); and
I built that in as an assumption, without ever enforcing it with
a BUG to check.

>From that very time exceptions have been added, some with their own
serialization, some with none, so that now it's all too messy to fix
without a leadin time for weeding out and and trying (with uncertain
success) to rework its usage in miscellaneous filesystems (including
fuse, nfs, spufs, others and gpu/drm/i915 use of shmobjects).

>
> thread1: going through a big range, stops in the middle of a vma and
> stores the restart address in vm_truncate_count.
>
> thread2: comes in with a small (e.g. single page) unmap request on
> the same vma, somewhere before restart_address, finds that the
> vma was already unmapped up to the restart address and happily
> returns without doing anything.

We could probably hack something in cheaply to fix that part of it.

>
> Another scenario would be two big unmap requests, both having to
> restart the unmapping and each one setting vm_truncate_count to its
> own value. This could go on forever without any of them being able to
> finish.

But I don't know how to fix this part without proper serialization.

>
> Truncate and hole punching already serialize with i_mutex. Other
> callers of unmap_mapping_range() do not, and it's difficult to get
> i_mutex protection for all callers. In particular ->d_revalidate(),
> which calls invalidate_inode_pages2_range() in fuse, may be called
> with or without i_mutex.
>
> This patch adds a new mutex to 'struct address_space' to prevent
> running multiple concurrent unmap_mapping_range() on the same mapping.

Yes, I once had hopes to reuse i_alloc_sem for this purpose; but
it's taken outside of mmap_sem and this needs to be taken inside.

>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
> Reported-by: Michael Leun <lkml20101129@xxxxxxxxxxxxxxx>
> Reported-by: Gurudas Pai <gurudas.pai@xxxxxxxxxx>
> Tested-by: Gurudas Pai <gurudas.pai@xxxxxxxxxx>

Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx

I just tried again, and failed again, to come up with a better answer:
thanks for persisting, Miklos.

> ---
> fs/gfs2/main.c | 9 +--------
> fs/inode.c | 22 +++++++++++++++-------
> fs/nilfs2/btnode.c | 5 -----
> fs/nilfs2/btnode.h | 1 -
> fs/nilfs2/mdt.c | 4 ++--
> fs/nilfs2/page.c | 13 -------------
> fs/nilfs2/page.h | 1 -
> fs/nilfs2/super.c | 2 +-
> include/linux/fs.h | 2 ++
> mm/memory.c | 2 ++
> 10 files changed, 23 insertions(+), 38 deletions(-)
>
> Index: linux-2.6/mm/memory.c
> ===================================================================
> --- linux-2.6.orig/mm/memory.c 2011-02-22 11:05:15.000000000 +0100
> +++ linux-2.6/mm/memory.c 2011-02-23 13:35:30.000000000 +0100
> @@ -2648,6 +2648,7 @@ void unmap_mapping_range(struct address_
> details.last_index = ULONG_MAX;
> details.i_mmap_lock = &mapping->i_mmap_lock;
>
> + mutex_lock(&mapping->unmap_mutex);
> spin_lock(&mapping->i_mmap_lock);
>
> /* Protect against endless unmapping loops */
> @@ -2664,6 +2665,7 @@ void unmap_mapping_range(struct address_
> if (unlikely(!list_empty(&mapping->i_mmap_nonlinear)))
> unmap_mapping_range_list(&mapping->i_mmap_nonlinear, &details);
> spin_unlock(&mapping->i_mmap_lock);
> + mutex_unlock(&mapping->unmap_mutex);
> }
> EXPORT_SYMBOL(unmap_mapping_range);
>
> Index: linux-2.6/fs/gfs2/main.c
> ===================================================================
> --- linux-2.6.orig/fs/gfs2/main.c 2011-02-22 11:05:15.000000000 +0100
> +++ linux-2.6/fs/gfs2/main.c 2011-02-23 13:35:30.000000000 +0100
> @@ -59,14 +59,7 @@ static void gfs2_init_gl_aspace_once(voi
> struct address_space *mapping = (struct address_space *)(gl + 1);
>
> gfs2_init_glock_once(gl);
> - memset(mapping, 0, sizeof(*mapping));
> - INIT_RADIX_TREE(&mapping->page_tree, GFP_ATOMIC);
> - spin_lock_init(&mapping->tree_lock);
> - spin_lock_init(&mapping->i_mmap_lock);
> - INIT_LIST_HEAD(&mapping->private_list);
> - spin_lock_init(&mapping->private_lock);
> - INIT_RAW_PRIO_TREE_ROOT(&mapping->i_mmap);
> - INIT_LIST_HEAD(&mapping->i_mmap_nonlinear);
> + address_space_init_once(mapping);
> }
>
> /**
> Index: linux-2.6/fs/inode.c
> ===================================================================
> --- linux-2.6.orig/fs/inode.c 2011-01-20 13:28:34.000000000 +0100
> +++ linux-2.6/fs/inode.c 2011-02-23 13:35:30.000000000 +0100
> @@ -295,6 +295,20 @@ static void destroy_inode(struct inode *
> call_rcu(&inode->i_rcu, i_callback);
> }
>
> +void address_space_init_once(struct address_space *mapping)
> +{
> + memset(mapping, 0, sizeof(*mapping));
> + INIT_RADIX_TREE(&mapping->page_tree, GFP_ATOMIC);
> + spin_lock_init(&mapping->tree_lock);
> + spin_lock_init(&mapping->i_mmap_lock);
> + INIT_LIST_HEAD(&mapping->private_list);
> + spin_lock_init(&mapping->private_lock);
> + INIT_RAW_PRIO_TREE_ROOT(&mapping->i_mmap);
> + INIT_LIST_HEAD(&mapping->i_mmap_nonlinear);
> + mutex_init(&mapping->unmap_mutex);
> +}
> +EXPORT_SYMBOL(address_space_init_once);
> +
> /*
> * These are initializations that only need to be done
> * once, because the fields are idempotent across use
> @@ -308,13 +322,7 @@ void inode_init_once(struct inode *inode
> INIT_LIST_HEAD(&inode->i_devices);
> INIT_LIST_HEAD(&inode->i_wb_list);
> INIT_LIST_HEAD(&inode->i_lru);
> - INIT_RADIX_TREE(&inode->i_data.page_tree, GFP_ATOMIC);
> - spin_lock_init(&inode->i_data.tree_lock);
> - spin_lock_init(&inode->i_data.i_mmap_lock);
> - INIT_LIST_HEAD(&inode->i_data.private_list);
> - spin_lock_init(&inode->i_data.private_lock);
> - INIT_RAW_PRIO_TREE_ROOT(&inode->i_data.i_mmap);
> - INIT_LIST_HEAD(&inode->i_data.i_mmap_nonlinear);
> + address_space_init_once(&inode->i_data);
> i_size_ordered_init(inode);
> #ifdef CONFIG_FSNOTIFY
> INIT_HLIST_HEAD(&inode->i_fsnotify_marks);
> Index: linux-2.6/fs/nilfs2/btnode.c
> ===================================================================
> --- linux-2.6.orig/fs/nilfs2/btnode.c 2011-01-20 13:28:34.000000000 +0100
> +++ linux-2.6/fs/nilfs2/btnode.c 2011-02-23 13:35:30.000000000 +0100
> @@ -35,11 +35,6 @@
> #include "btnode.h"
>
>
> -void nilfs_btnode_cache_init_once(struct address_space *btnc)
> -{
> - nilfs_mapping_init_once(btnc);
> -}
> -
> static const struct address_space_operations def_btnode_aops = {
> .sync_page = block_sync_page,
> };
> Index: linux-2.6/fs/nilfs2/btnode.h
> ===================================================================
> --- linux-2.6.orig/fs/nilfs2/btnode.h 2011-01-20 13:28:34.000000000 +0100
> +++ linux-2.6/fs/nilfs2/btnode.h 2011-02-23 13:35:30.000000000 +0100
> @@ -37,7 +37,6 @@ struct nilfs_btnode_chkey_ctxt {
> struct buffer_head *newbh;
> };
>
> -void nilfs_btnode_cache_init_once(struct address_space *);
> void nilfs_btnode_cache_init(struct address_space *, struct backing_dev_info *);
> void nilfs_btnode_cache_clear(struct address_space *);
> struct buffer_head *nilfs_btnode_create_block(struct address_space *btnc,
> Index: linux-2.6/fs/nilfs2/mdt.c
> ===================================================================
> --- linux-2.6.orig/fs/nilfs2/mdt.c 2011-01-20 13:28:34.000000000 +0100
> +++ linux-2.6/fs/nilfs2/mdt.c 2011-02-23 13:35:30.000000000 +0100
> @@ -454,9 +454,9 @@ int nilfs_mdt_setup_shadow_map(struct in
> struct backing_dev_info *bdi = inode->i_sb->s_bdi;
>
> INIT_LIST_HEAD(&shadow->frozen_buffers);
> - nilfs_mapping_init_once(&shadow->frozen_data);
> + address_space_init_once(&shadow->frozen_data);
> nilfs_mapping_init(&shadow->frozen_data, bdi, &shadow_map_aops);
> - nilfs_mapping_init_once(&shadow->frozen_btnodes);
> + address_space_init_once(&shadow->frozen_btnodes);
> nilfs_mapping_init(&shadow->frozen_btnodes, bdi, &shadow_map_aops);
> mi->mi_shadow = shadow;
> return 0;
> Index: linux-2.6/fs/nilfs2/page.c
> ===================================================================
> --- linux-2.6.orig/fs/nilfs2/page.c 2011-01-20 13:28:34.000000000 +0100
> +++ linux-2.6/fs/nilfs2/page.c 2011-02-23 13:35:30.000000000 +0100
> @@ -492,19 +492,6 @@ unsigned nilfs_page_count_clean_buffers(
> return nc;
> }
>
> -void nilfs_mapping_init_once(struct address_space *mapping)
> -{
> - memset(mapping, 0, sizeof(*mapping));
> - INIT_RADIX_TREE(&mapping->page_tree, GFP_ATOMIC);
> - spin_lock_init(&mapping->tree_lock);
> - INIT_LIST_HEAD(&mapping->private_list);
> - spin_lock_init(&mapping->private_lock);
> -
> - spin_lock_init(&mapping->i_mmap_lock);
> - INIT_RAW_PRIO_TREE_ROOT(&mapping->i_mmap);
> - INIT_LIST_HEAD(&mapping->i_mmap_nonlinear);
> -}
> -
> void nilfs_mapping_init(struct address_space *mapping,
> struct backing_dev_info *bdi,
> const struct address_space_operations *aops)
> Index: linux-2.6/fs/nilfs2/page.h
> ===================================================================
> --- linux-2.6.orig/fs/nilfs2/page.h 2011-01-20 13:28:34.000000000 +0100
> +++ linux-2.6/fs/nilfs2/page.h 2011-02-23 13:35:30.000000000 +0100
> @@ -61,7 +61,6 @@ void nilfs_free_private_page(struct page
> int nilfs_copy_dirty_pages(struct address_space *, struct address_space *);
> void nilfs_copy_back_pages(struct address_space *, struct address_space *);
> void nilfs_clear_dirty_pages(struct address_space *);
> -void nilfs_mapping_init_once(struct address_space *mapping);
> void nilfs_mapping_init(struct address_space *mapping,
> struct backing_dev_info *bdi,
> const struct address_space_operations *aops);
> Index: linux-2.6/fs/nilfs2/super.c
> ===================================================================
> --- linux-2.6.orig/fs/nilfs2/super.c 2011-02-07 17:05:19.000000000 +0100
> +++ linux-2.6/fs/nilfs2/super.c 2011-02-23 13:35:30.000000000 +0100
> @@ -1279,7 +1279,7 @@ static void nilfs_inode_init_once(void *
> #ifdef CONFIG_NILFS_XATTR
> init_rwsem(&ii->xattr_sem);
> #endif
> - nilfs_btnode_cache_init_once(&ii->i_btnode_cache);
> + address_space_init_once(&ii->i_btnode_cache);
> ii->i_bmap = &ii->i_bmap_data;
> inode_init_once(&ii->vfs_inode);
> }
> Index: linux-2.6/include/linux/fs.h
> ===================================================================
> --- linux-2.6.orig/include/linux/fs.h 2011-02-22 11:04:39.000000000 +0100
> +++ linux-2.6/include/linux/fs.h 2011-02-23 13:35:30.000000000 +0100
> @@ -649,6 +649,7 @@ struct address_space {
> spinlock_t private_lock; /* for use by the address_space */
> struct list_head private_list; /* ditto */
> struct address_space *assoc_mapping; /* ditto */
> + struct mutex unmap_mutex; /* to protect unmapping */
> } __attribute__((aligned(sizeof(long))));
> /*
> * On most architectures that alignment is already the case; but
> @@ -2225,6 +2226,7 @@ extern loff_t vfs_llseek(struct file *fi
>
> extern int inode_init_always(struct super_block *, struct inode *);
> extern void inode_init_once(struct inode *);
> +extern void address_space_init_once(struct address_space *mapping);
> extern void ihold(struct inode * inode);
> extern void iput(struct inode *);
> extern struct inode * igrab(struct inode *);
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