On Tue, 7 May 2013 10:52:05 -0700
Colin Cross <ccross@xxxxxxxxxxx> wrote:
> CIFS calls wait_event_freezekillable_unsafe with a VFS lock held,
> which is unsafe and will cause lockdep warnings when 6aa9707
> "lockdep: check that no locks held at freeze time" is reapplied
> (it was reverted in dbf520a). CIFS shouldn't be doing this, but
> it has long-running syscalls that must hold a lock but also
> shouldn't block suspend. Until CIFS freeze handling is rewritten
> to use a signal to exit out of the critical section, add a new
> wait_event_freezekillable_unsafe helper that will not run the
> lockdep test when 6aa9707 is reapplied, and call it from CIFS.
>
> In practice the likley result of holding the lock while freezing
> is that a second task blocked on the lock will never freeze,
> aborting suspend, but it is possible to manufacture a case using
> the cgroup freezer, the lock, and the suspend freezer to create
> a deadlock. Silencing the lockdep warning here will allow
> problems to be found in other drivers that may have a more
> serious deadlock risk, and prevent new problems from being added.
>
> Acked-by: Pavel Machek <pavel@xxxxxx>
> Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx>
> ---
> v4:
> Corrected to include CIFS wait_for_response hunk.
> The rest of this series is still at v3.
>
> fs/cifs/transport.c | 2 +-
> include/linux/freezer.h | 13 +++++++++++++
> 2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
> index 1a52868..e7f22f8 100644
> --- a/fs/cifs/transport.c
> +++ b/fs/cifs/transport.c
> @@ -452,7 +452,7 @@ wait_for_response(struct TCP_Server_Info *server, struct mid_q_entry *midQ)
> {
> int error;
>
> - error = wait_event_freezekillable(server->response_q,
> + error = wait_event_freezekillable_unsafe(server->response_q,
> midQ->mid_state != MID_REQUEST_SUBMITTED);
> if (error < 0)
> return -ERESTARTSYS;
> diff --git a/include/linux/freezer.h b/include/linux/freezer.h
> index 5b31e21c..d3c038e 100644
> --- a/include/linux/freezer.h
> +++ b/include/linux/freezer.h
> @@ -212,6 +212,16 @@ static inline bool freezer_should_skip(struct task_struct *p)
> __retval; \
> })
>
> +/* DO NOT ADD ANY NEW CALLERS OF THIS FUNCTION */
> +#define wait_event_freezekillable_unsafe(wq, condition) \
> +({ \
> + int __retval; \
> + freezer_do_not_count(); \
> + __retval = wait_event_killable(wq, (condition)); \
> + freezer_count_unsafe(); \
> + __retval; \
> +})
> +
> #define wait_event_freezable(wq, condition) \
> ({ \
> int __retval; \
> @@ -277,6 +287,9 @@ static inline void set_freezable(void) {}
> #define wait_event_freezekillable(wq, condition) \
> wait_event_killable(wq, condition)
>
> +#define wait_event_freezekillable_unsafe(wq, condition) \
> + wait_event_killable(wq, condition)
> +
> #endif /* !CONFIG_FREEZER */
>
> #endif /* FREEZER_H_INCLUDED */
Looks fine...
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
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