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SubjectRe: [PATCH 3/4] eventfd: make operations on eventfd return -EIDRM if it's hung up
On 2013/2/3 0:12, Kirill A. Shutemov wrote:
> On Sat, Feb 02, 2013 at 02:51:30PM +0800, Li Zefan wrote:
>> Currently when a cgroup is removed, it calls eventfd_signal() for
>> each registered cgroup event, so userspace can be notified and blocked
>> reads can be unblocked.
>>
>> The problem is, if we have multiple threads blocked on the same eventfd,
>> only one of them will be unlocked.
>>
>> This patch makes sure all operations on the same eventfd can be unbocked.
>>
>> There's another problem, a new cgroup event can be registered while we
>> are removing the cgroup, and then reading the eventfd will be blocked
>> until the thread is killed. This patch also fixes this issue.
>>
>> Signed-off-by: Li Zefan <lizefan@huawei.com>
>> ---
>> fs/eventfd.c | 23 +++++++++++++++++++++--
>> kernel/cgroup.c | 1 -
>> 2 files changed, 21 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/eventfd.c b/fs/eventfd.c
>> index acf15e3..48de15a 100644
>> --- a/fs/eventfd.c
>> +++ b/fs/eventfd.c
>> @@ -35,6 +35,7 @@ struct eventfd_ctx {
>> */
>> __u64 count;
>> unsigned int flags;
>> + bool hung_up;
>> };
>>
>> /**
>> @@ -71,11 +72,19 @@ EXPORT_SYMBOL_GPL(eventfd_signal);
>> * eventfd_signal_hangup - Notify that this eventfd is hung up.
>> * @ctx: [in] Pointer to the eventfd context.
>> *
>> - * Issue a POLLHUP wakeup.
>> + * Issue a POLLHUP wakeup. All current blocked reads, writes and polls on
>> + * this eventfd will return with -EIDRM. Future operations on it will also
>> + * return with -EDIRM.
>> */
>> void eventfd_signal_hangup(struct eventfd_ctx *ctx)
>> {
>> - wake_up_poll(&ctx->wqh, POLLHUP);
>> + unsigned long flags;
>> +
>> + spin_lock_irqsave(&ctx->wqh.lock, flags);
>> + ctx->hung_up = true;
>> + if (waitqueue_active(&ctx->wqh))
>> + wake_up_locked_poll(&ctx->wqh, POLLHUP);
>> + spin_unlock_irqrestore(&ctx->wqh.lock, flags);
>> }
>>
>> static void eventfd_free_ctx(struct eventfd_ctx *ctx)
>> @@ -140,6 +149,8 @@ static unsigned int eventfd_poll(struct file *file, poll_table *wait)
>> events |= POLLERR;
>> if (ULLONG_MAX - 1 > ctx->count)
>> events |= POLLOUT;
>> + if (ctx->hung_up)
>> + events |= POLLHUP;
>> spin_unlock_irqrestore(&ctx->wqh.lock, flags);
>>
>> return events;
>> @@ -208,6 +219,10 @@ ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt)
>> __add_wait_queue(&ctx->wqh, &wait);
>> for (;;) {
>> set_current_state(TASK_INTERRUPTIBLE);
>> + if (ctx->hung_up) {
>> + res = -EIDRM;
>> + break;
>> + }
>
> Shouldn't we just return indicate end-of-file if ctx->hung_up?
>

makes sense

>> if (ctx->count > 0) {
>> res = 0;
>> break;
>> @@ -272,6 +287,10 @@ static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t c
>> __add_wait_queue(&ctx->wqh, &wait);
>> for (res = 0;;) {
>> set_current_state(TASK_INTERRUPTIBLE);
>> + if (ctx->hung_up) {
>> + res = -EIDRM;
>
> -EPIPE?
>

I wan't sure which errno is most appropriate, but EPIPE seems better.

>> + break;
>> + }
>> if (ULLONG_MAX - ctx->count > ucnt) {
>> res = sizeof(ucnt);
>> break;
>> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
>> index a3d361b..fcb1ab6 100644
>> --- a/kernel/cgroup.c
>> +++ b/kernel/cgroup.c
>> @@ -4373,7 +4373,6 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
>> ctx = eventfd_ctx_get(event->eventfd);
>> spin_unlock(&cgrp->event_list_lock);
>>
>> - eventfd_signal(ctx, 1);
>> eventfd_signal_hangup(ctx);
>> eventfd_ctx_put(ctx);
>>
>> --
>> 1.8.0.2
>> --
>> To unsubscribe from this list: send the line "unsubscribe cgroups" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>



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