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SubjectRe: [PATCH] TOMOYO: Use RCU primitives for list operation
Quoting Tetsuo Handa (penguin-kernel@I-love.SAKURA.ne.jp):
> [PATCH] TOMOYO: Use RCU primitives for list operation
>
> Remove down_read()/up_read() by replacing with RCU primitives.
> SRCU based garbage collector will be added in the future.
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> ---
> security/tomoyo/common.c | 52 ++++++++++-----------------------------------
> security/tomoyo/common.h | 14 ++++++------
> security/tomoyo/domain.c | 38 ++++++++++----------------------
> security/tomoyo/file.c | 50 ++++++++++++++-----------------------------
> security/tomoyo/realpath.c | 4 ---
> 5 files changed, 49 insertions(+), 109 deletions(-)
>
> --- security-testing-2.6.orig/security/tomoyo/common.c
> +++ security-testing-2.6/security/tomoyo/common.c
> @@ -365,9 +365,6 @@ bool tomoyo_is_domain_def(const unsigned
> *
> * @domainname: The domainname to find.
> *
> - * Caller must call down_read(&tomoyo_domain_list_lock); or
> - * down_write(&tomoyo_domain_list_lock); .
> - *
> * Returns pointer to "struct tomoyo_domain_info" if found, NULL otherwise.
> */
> struct tomoyo_domain_info *tomoyo_find_domain(const char *domainname)
> @@ -377,7 +374,7 @@ struct tomoyo_domain_info *tomoyo_find_d
>
> name.name = domainname;
> tomoyo_fill_path_info(&name);
> - list_for_each_entry(domain, &tomoyo_domain_list, list) {
> + list_for_each_entry_rcu(domain, &tomoyo_domain_list, list) {
> if (!domain->is_deleted &&
> !tomoyo_pathcmp(&name, domain->domainname))
> return domain;
> @@ -837,8 +834,7 @@ bool tomoyo_domain_quota_is_ok(struct to
>
> if (!domain)
> return true;
> - down_read(&tomoyo_domain_acl_info_list_lock);
> - list_for_each_entry(ptr, &domain->acl_info_list, list) {
> + list_for_each_entry_rcu(ptr, &domain->acl_info_list, list) {
> if (ptr->type & TOMOYO_ACL_DELETED)
> continue;
> switch (tomoyo_acl_type2(ptr)) {

You are removing the down_read()s, but not replacing them with
rcu_read_lock()s. I assume this is based on the same discussions
you had with Paul awhile ago about the safety of walking the list
bc you only append to the end (which I trust must have concluded
in your favor)?

If you'll be adding gc eventually anyway, is it really worthwhile
to 'violate the rules' now by calling list_for_each_entry_rcu()
without being inside rcu_read_lock() now? I fear it'll only serve
to confuse readers, especially those looking for rcu users to serve
as examples.

-serge


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