2010/12/14 Mike Waychison <mikew@xxxxxxxxxx>:
> The netconsole driver currently doesn't do any locking over its
> configuration fields. This can cause problems if we were to ever have
> concurrent writing to fields while somebody is enabling the service.
>
> For simplicity, this patch extends targets_list_lock to cover all
> configuration fields within the targets. Macros are also added here to
> wrap accessors so that we check whether the target has been enabled with
> locking handled.
>
> Signed-off-by: Mike Waychison <mikew@xxxxxxxxxx>
> Acked-by: Matt Mackall <mpm@xxxxxxxxxxx>
> ---
> drivers/net/netconsole.c | 114 ++++++++++++++++++++++++++--------------------
> 1 files changed, 64 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index c87a49e..6e16888 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
> @@ -327,6 +327,7 @@ static ssize_t store_enabled(struct netconsole_target *nt,
> const char *buf,
> size_t count)
> {
> + unsigned long flags;
> int err;
> long enabled;
>
> @@ -335,6 +336,10 @@ static ssize_t store_enabled(struct netconsole_target *nt,
> return enabled;
>
> if (enabled) { /* 1 */
> + spin_lock_irqsave(&target_list_lock, flags);
> + if (nt->enabled)
> + goto busy;
> + spin_unlock_irqrestore(&target_list_lock, flags);
>
This looks wrong. Unless there is another lock or mutex covering this
function, at this point (after spin_unlock_irqrestore()) another
thread might set nt->enabled = 1.
Best Regards,
Michał Mirosław
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