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anon_inodes: use fops->owner for module refcount

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There is an imbalance for anonymous inodes. If the fops->owner field is set,
the module reference count of owner is decreases on release.
("filp_close" --> "__fput" ---> "fops_put")

On the other hand, anon_inode_getfd does not increase the module reference
count of owner. This causes two problems:

- if owner is set, the module refcount goes negative
- if owner is not set, the module can be unloaded while code is running

This patch changes anon_inode_getfd to be symmetric regarding fops->owner
handling.

I have checked all existing users of anon_inode_getfd. Noone sets fops->owner,
thats why nobody has seen the module refcount negative. The refcounting was
tested with a patched and unpatched KVM module.(see patch 2/2) I also did an
epoll_open/close test.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Christian Borntraeger 2008-12-02 11:16:03 +01:00 committed by Avi Kivity
parent e93353c93a
commit e3a2a0d4e5
1 changed files with 6 additions and 1 deletions
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7
fs/anon_inodes.c
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@ -79,9 +79,12 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops,
if (IS_ERR(anon_inode_inode))
return -ENODEV;
if (fops->owner && !try_module_get(fops->owner))
return -ENOENT;
error = get_unused_fd_flags(flags);
if (error < 0)
return error;
goto err_module;
fd = error;
/*
@ -128,6 +131,8 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops,
dput(dentry);
err_put_unused_fd:
put_unused_fd(fd);
err_module:
module_put(fops->owner);
return error;
}
EXPORT_SYMBOL_GPL(anon_inode_getfd);