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Date: Tue, 2 Dec 2008 11:16:03 +0100 From: Christian Borntraeger <borntraeger@...ibm.com> To: Avi Kivity <avi@...hat.com> Cc: kvm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, Davide Libenzi <davidel@...ilserver.org> Subject: [PATCH 1/2] anon_inodes: use fops->owner for module refcount 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@...ibm.com> Reviewed-by: Davide Libenzi <davidel@...ilserver.org> --- fs/anon_inodes.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) Index: kvm/fs/anon_inodes.c =================================================================== --- kvm.orig/fs/anon_inodes.c +++ kvm/fs/anon_inodes.c @@ -79,9 +79,12 @@ int anon_inode_getfd(const char *name, c 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 @@ err_dput: dput(dentry); err_put_unused_fd: put_unused_fd(fd); +err_module: + module_put(fops->owner); return error; } EXPORT_SYMBOL_GPL(anon_inode_getfd); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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