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Subject[PATCH v2] fuse: fix deadlock between atomic O_TRUNC open() and page invalidations
Date
fuse_finish_open() will be called with FUSE_NOWRITE set in case of atomic
O_TRUNC open(), so commit 76224355db75 ("fuse: truncate pagecache on
atomic_o_trunc") replaced invalidate_inode_pages2() by truncate_pagecache()
in such a case to avoid the A-A deadlock. However, we found another A-B-B-A
deadlock related to the case above, which will cause the xfstests
generic/464 testcase hung in our virtio-fs test environment.

For example, consider two processes concurrently open one same file, one
with O_TRUNC and another without O_TRUNC. The deadlock case is described
below, if open(O_TRUNC) is already set_nowrite(acquired A), and is trying
to lock a page (acquiring B), open() could have held the page lock
(acquired B), and waiting on the page writeback (acquiring A). This would
lead to deadlocks.

open(O_TRUNC)
----------------------------------------------------------------
fuse_open_common
inode_lock [C acquire]
fuse_set_nowrite [A acquire]

fuse_finish_open
truncate_pagecache
lock_page [B acquire]
truncate_inode_page
unlock_page [B release]

fuse_release_nowrite [A release]
inode_unlock [C release]
----------------------------------------------------------------

open()
----------------------------------------------------------------
fuse_open_common
fuse_finish_open
invalidate_inode_pages2
lock_page [B acquire]
fuse_launder_page
fuse_wait_on_page_writeback [A acquire & release]
unlock_page [B release]
----------------------------------------------------------------

Besides this case, all calls of invalidate_inode_pages2() and
invalidate_inode_pages2_range() in fuse code also can deadlock with
open(O_TRUNC). This commit tries to fix it by adding a new lock,
atomic_o_trunc, to protect the areas with the A-B-B-A deadlock risk.

Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
---
fs/fuse/dax.c | 4 ++--
fs/fuse/dir.c | 2 +-
fs/fuse/file.c | 28 ++++++++++++++++++++++++++--
fs/fuse/fuse_i.h | 7 +++++++
fs/fuse/inode.c | 7 ++++---
5 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
index 182b24a14804..e5203d61698c 100644
--- a/fs/fuse/dax.c
+++ b/fs/fuse/dax.c
@@ -878,11 +878,11 @@ static int dmap_writeback_invalidate(struct inode *inode,
return ret;
}

- ret = invalidate_inode_pages2_range(inode->i_mapping,
+ ret = fuse_invalidate_inode_pages_range(inode,
start_pos >> PAGE_SHIFT,
end_pos >> PAGE_SHIFT);
if (ret)
- pr_debug("fuse: invalidate_inode_pages2_range() failed err=%d\n",
+ pr_debug("fuse: fuse_invalidate_inode_pages_range() failed err=%d\n",
ret);

return ret;
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 656e921f3506..d6d5dcd3cf1e 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1778,7 +1778,7 @@ int fuse_do_setattr(struct dentry *dentry, struct iattr *attr,
if ((is_truncate || !is_wb) &&
S_ISREG(inode->i_mode) && oldsize != outarg.attr.size) {
truncate_pagecache(inode, outarg.attr.size);
- invalidate_inode_pages2(mapping);
+ fuse_invalidate_inode_pages(inode);
}

clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 829094451774..1dde21bad53c 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -124,6 +124,28 @@ static void fuse_file_put(struct fuse_file *ff, bool sync, bool isdir)
}
}

+int fuse_invalidate_inode_pages_range(struct inode *inode, pgoff_t start,
+ pgoff_t end)
+{
+ int ret;
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ bool may_truncate = fc->atomic_o_trunc &&
+ (fc->writeback_cache || FUSE_IS_DAX(inode));
+
+ if (may_truncate)
+ mutex_lock(&get_fuse_inode(inode)->atomic_trunc_mutex);
+ ret = invalidate_inode_pages2_range(inode->i_mapping, start, end);
+ if (may_truncate)
+ mutex_unlock(&get_fuse_inode(inode)->atomic_trunc_mutex);
+
+ return ret;
+}
+
+int fuse_invalidate_inode_pages(struct inode *inode)
+{
+ return fuse_invalidate_inode_pages_range(inode, 0, -1);
+}
+
struct fuse_file *fuse_file_open(struct fuse_mount *fm, u64 nodeid,
unsigned int open_flags, bool isdir)
{
@@ -214,7 +236,7 @@ void fuse_finish_open(struct inode *inode, struct file *file)
file_update_time(file);
fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
} else if (!(ff->open_flags & FOPEN_KEEP_CACHE)) {
- invalidate_inode_pages2(inode->i_mapping);
+ fuse_invalidate_inode_pages(inode);
}

if ((file->f_mode & FMODE_WRITE) && fc->writeback_cache)
@@ -241,6 +263,7 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)

if (is_wb_truncate || dax_truncate) {
inode_lock(inode);
+ mutex_lock(&get_fuse_inode(inode)->atomic_trunc_mutex);
fuse_set_nowrite(inode);
}

@@ -261,6 +284,7 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)

if (is_wb_truncate | dax_truncate) {
fuse_release_nowrite(inode);
+ mutex_unlock(&get_fuse_inode(inode)->atomic_trunc_mutex);
inode_unlock(inode);
}

@@ -2408,7 +2432,7 @@ static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)
if (vma->vm_flags & VM_MAYSHARE)
return -ENODEV;

- invalidate_inode_pages2(file->f_mapping);
+ fuse_invalidate_inode_pages(file_inode(file));

return generic_file_mmap(file, vma);
}
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index e8e59fbdefeb..ea293d0347a0 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -149,6 +149,9 @@ struct fuse_inode {
/** Lock to protect write related fields */
spinlock_t lock;

+ /** Lock for serializing page invalidation and atomic_o_trunc open */
+ struct mutex atomic_trunc_mutex;
+
#ifdef CONFIG_FUSE_DAX
/*
* Dax specific inode data
@@ -1315,4 +1318,8 @@ struct fuse_file *fuse_file_open(struct fuse_mount *fm, u64 nodeid,
void fuse_file_release(struct inode *inode, struct fuse_file *ff,
unsigned int open_flags, fl_owner_t id, bool isdir);

+int fuse_invalidate_inode_pages(struct inode *inode);
+int fuse_invalidate_inode_pages_range(struct inode *inode,
+ pgoff_t start, pgoff_t end);
+
#endif /* _FS_FUSE_I_H */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index ee846ce371d8..997c620f25df 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -86,6 +86,7 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
fi->state = 0;
mutex_init(&fi->mutex);
spin_lock_init(&fi->lock);
+ mutex_init(&fi->atomic_trunc_mutex);
fi->forget = fuse_alloc_forget();
if (!fi->forget)
goto out_free;
@@ -107,6 +108,7 @@ static void fuse_free_inode(struct inode *inode)
struct fuse_inode *fi = get_fuse_inode(inode);

mutex_destroy(&fi->mutex);
+ mutex_destroy(&fi->atomic_trunc_mutex);
kfree(fi->forget);
#ifdef CONFIG_FUSE_DAX
kfree(fi->dax);
@@ -299,7 +301,7 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
}

if (inval)
- invalidate_inode_pages2(inode->i_mapping);
+ fuse_invalidate_inode_pages(inode);
}

if (IS_ENABLED(CONFIG_FUSE_DAX))
@@ -448,8 +450,7 @@ int fuse_reverse_inval_inode(struct fuse_conn *fc, u64 nodeid,
pg_end = -1;
else
pg_end = (offset + len - 1) >> PAGE_SHIFT;
- invalidate_inode_pages2_range(inode->i_mapping,
- pg_start, pg_end);
+ fuse_invalidate_inode_pages_range(inode, pg_start, pg_end);
}
iput(inode);
return 0;
--
2.20.1
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