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SubjectRe: [PATCH] hysdn: fix to a race condition in put_log_buffer
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Hello!

On 08/03/2017 02:33 PM, Anton Volkov wrote:

> The synchronization type that was used earlier to guard the loop that
> deletes unused log buffers may lead to a situation that prevents any
> thread from going through the loop.
>
> The patch deletes previously used synchronization mechanism and moves
> the loop under the spin_lock so the similar cases won't be feasible in
> the future.
>
> Found by by Linux Driver Verification project (linuxtesting.org).
>
> Signed-off-by: Anton Volkov <avolkov@ispras.ru>
> ---
> drivers/isdn/hysdn/hysdn_proclog.c | 27 ++++++++++++---------------
> 1 file changed, 12 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/isdn/hysdn/hysdn_proclog.c b/drivers/isdn/hysdn/hysdn_proclog.c
> index 7b5fd8f..b152c6c 100644
> --- a/drivers/isdn/hysdn/hysdn_proclog.c
> +++ b/drivers/isdn/hysdn/hysdn_proclog.c
[...]
> else
> pd->log_tail->next = ib; /* follows existing messages */
> pd->log_tail = ib; /* new tail */
> - i = pd->del_lock++; /* get lock state */
> - spin_unlock_irqrestore(&card->hysdn_lock, flags);
>
> /* delete old entrys */
> - if (!i)
> - while (pd->log_head->next) {
> - if ((pd->log_head->usage_cnt <= 0) &&
> - (pd->log_head->next->usage_cnt <= 0)) {
> - ib = pd->log_head;
> - pd->log_head = pd->log_head->next;
> - kfree(ib);
> - } else
> - break;
> - } /* pd->log_head->next */
> - pd->del_lock--; /* release lock level */
> + while (pd->log_head->next) {
> + if ((pd->log_head->usage_cnt <= 0) &&
> + (pd->log_head->next->usage_cnt <= 0)) {
> + ib = pd->log_head;
> + pd->log_head = pd->log_head->next;
> + kfree(ib);
> + } else
> + break;
> + } /* pd->log_head->next */

Need {} in the *else* branch as *if* had them.

[...]

MBR, Sergei

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