From: Petr Mladek <pmladek@suse.com> To: Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Tejun Heo <tj@kernel.org>, Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Josh Triplett <josh@joshtriplett.org>, Thomas Gleixner <tglx@linutronix.de>, Linus Torvalds <torvalds@linux-foundation.org>, Jiri Kosina <jkosina@suse.cz>, Borislav Petkov <bp@suse.de>, Michal Hocko <mhocko@suse.cz>, linux-mm@kvack.org, Vlastimil Babka <vbabka@suse.cz>, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com> Subject: [PATCH v4 07/22] kthread: Detect when a kthread work is used by more workers Date: Mon, 25 Jan 2016 16:44:56 +0100 [thread overview] Message-ID: <1453736711-6703-8-git-send-email-pmladek@suse.com> (raw) In-Reply-To: <1453736711-6703-1-git-send-email-pmladek@suse.com> Nothing currently prevents a work from queuing for a kthread worker when it is already running on another one. This means that the work might run in parallel on more workers. Also some operations, e.g. flush or drain are not reliable. This problem will be even more visible after we add cancel_kthread_work() function. It will only have "work" as the parameter and will use worker->lock to synchronize with others. Well, normally this is not a problem because the API users are sane. But bugs might happen and users also might be crazy. This patch adds a warning when we try to insert the work for another worker. It does not fully prevent the misuse because it would make the code much more complicated without a big benefit. A side effect is that one needs to explicitely reinitialize the work if it must be queued into another worker. This is needed, for example, when the worker is stopped and started again. It is a bit inconvenient. But it looks like a good compromise between the stability and complexity. Just for completeness, the patch adds a check for disabled interrupts and an empty queue. The patch also puts all the checks into a separate function. It will be reused when implementing delayed works. Signed-off-by: Petr Mladek <pmladek@suse.com> --- kernel/kthread.c | 28 +++++++++++++++++++++++++--- 1 file changed, 25 insertions(+), 3 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index 1d41e0faef2d..e12576bc0e39 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -574,6 +574,9 @@ EXPORT_SYMBOL_GPL(__init_kthread_worker); * The works are not allowed to keep any locks, disable preemption or interrupts * when they finish. There is defined a safe point for freezing when one work * finishes and before a new one is started. + * + * Also the works must not be handled by more workers at the same time, see also + * queue_kthread_work(). */ int kthread_worker_fn(void *worker_ptr) { @@ -696,12 +699,22 @@ create_kthread_worker_on_cpu(int cpu, const char namefmt[]) } EXPORT_SYMBOL(create_kthread_worker_on_cpu); +static void insert_kthread_work_sanity_check(struct kthread_worker *worker, + struct kthread_work *work) +{ + lockdep_assert_held(&worker->lock); + WARN_ON_ONCE(!irqs_disabled()); + WARN_ON_ONCE(!list_empty(&work->node)); + /* Do not use a work with more workers, see queue_kthread_work() */ + WARN_ON_ONCE(work->worker && work->worker != worker); +} + /* insert @work before @pos in @worker */ static void insert_kthread_work(struct kthread_worker *worker, - struct kthread_work *work, - struct list_head *pos) + struct kthread_work *work, + struct list_head *pos) { - lockdep_assert_held(&worker->lock); + insert_kthread_work_sanity_check(worker, work); list_add_tail(&work->node, pos); work->worker = worker; @@ -717,6 +730,15 @@ static void insert_kthread_work(struct kthread_worker *worker, * Queue @work to work processor @task for async execution. @task * must have been created with kthread_worker_create(). Returns %true * if @work was successfully queued, %false if it was already pending. + * + * Never queue a work into a worker when it is being processed by another + * one. Otherwise, some operations, e.g. cancel or flush, will not work + * correctly or the work might run in parallel. This is not enforced + * because it would make the code too complex. There are only warnings + * printed when such a situation is detected. + * + * Reinitialize the work if it needs to be used by another worker. + * For example, when the worker was stopped and started again. */ bool queue_kthread_work(struct kthread_worker *worker, struct kthread_work *work) -- 1.8.5.6
WARNING: multiple messages have this Message-ID (diff)
From: Petr Mladek <pmladek@suse.com> To: Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Tejun Heo <tj@kernel.org>, Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Josh Triplett <josh@joshtriplett.org>, Thomas Gleixner <tglx@linutronix.de>, Linus Torvalds <torvalds@linux-foundation.org>, Jiri Kosina <jkosina@suse.cz>, Borislav Petkov <bp@suse.de>, Michal Hocko <mhocko@suse.cz>, linux-mm@kvack.org, Vlastimil Babka <vbabka@suse.cz>, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com> Subject: [PATCH v4 07/22] kthread: Detect when a kthread work is used by more workers Date: Mon, 25 Jan 2016 16:44:56 +0100 [thread overview] Message-ID: <1453736711-6703-8-git-send-email-pmladek@suse.com> (raw) In-Reply-To: <1453736711-6703-1-git-send-email-pmladek@suse.com> Nothing currently prevents a work from queuing for a kthread worker when it is already running on another one. This means that the work might run in parallel on more workers. Also some operations, e.g. flush or drain are not reliable. This problem will be even more visible after we add cancel_kthread_work() function. It will only have "work" as the parameter and will use worker->lock to synchronize with others. Well, normally this is not a problem because the API users are sane. But bugs might happen and users also might be crazy. This patch adds a warning when we try to insert the work for another worker. It does not fully prevent the misuse because it would make the code much more complicated without a big benefit. A side effect is that one needs to explicitely reinitialize the work if it must be queued into another worker. This is needed, for example, when the worker is stopped and started again. It is a bit inconvenient. But it looks like a good compromise between the stability and complexity. Just for completeness, the patch adds a check for disabled interrupts and an empty queue. The patch also puts all the checks into a separate function. It will be reused when implementing delayed works. Signed-off-by: Petr Mladek <pmladek@suse.com> --- kernel/kthread.c | 28 +++++++++++++++++++++++++--- 1 file changed, 25 insertions(+), 3 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index 1d41e0faef2d..e12576bc0e39 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -574,6 +574,9 @@ EXPORT_SYMBOL_GPL(__init_kthread_worker); * The works are not allowed to keep any locks, disable preemption or interrupts * when they finish. There is defined a safe point for freezing when one work * finishes and before a new one is started. + * + * Also the works must not be handled by more workers at the same time, see also + * queue_kthread_work(). */ int kthread_worker_fn(void *worker_ptr) { @@ -696,12 +699,22 @@ create_kthread_worker_on_cpu(int cpu, const char namefmt[]) } EXPORT_SYMBOL(create_kthread_worker_on_cpu); +static void insert_kthread_work_sanity_check(struct kthread_worker *worker, + struct kthread_work *work) +{ + lockdep_assert_held(&worker->lock); + WARN_ON_ONCE(!irqs_disabled()); + WARN_ON_ONCE(!list_empty(&work->node)); + /* Do not use a work with more workers, see queue_kthread_work() */ + WARN_ON_ONCE(work->worker && work->worker != worker); +} + /* insert @work before @pos in @worker */ static void insert_kthread_work(struct kthread_worker *worker, - struct kthread_work *work, - struct list_head *pos) + struct kthread_work *work, + struct list_head *pos) { - lockdep_assert_held(&worker->lock); + insert_kthread_work_sanity_check(worker, work); list_add_tail(&work->node, pos); work->worker = worker; @@ -717,6 +730,15 @@ static void insert_kthread_work(struct kthread_worker *worker, * Queue @work to work processor @task for async execution. @task * must have been created with kthread_worker_create(). Returns %true * if @work was successfully queued, %false if it was already pending. + * + * Never queue a work into a worker when it is being processed by another + * one. Otherwise, some operations, e.g. cancel or flush, will not work + * correctly or the work might run in parallel. This is not enforced + * because it would make the code too complex. There are only warnings + * printed when such a situation is detected. + * + * Reinitialize the work if it needs to be used by another worker. + * For example, when the worker was stopped and started again. */ bool queue_kthread_work(struct kthread_worker *worker, struct kthread_work *work) -- 1.8.5.6 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-01-25 16:10 UTC|newest] Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-01-25 15:44 [PATCH v4 00/22] kthread: Use kthread worker API more widely Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 01/22] timer: Allow to check when the timer callback has not finished yet Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 18:44 ` Tejun Heo 2016-01-25 18:44 ` Tejun Heo 2016-01-25 15:44 ` [PATCH v4 02/22] kthread/smpboot: Do not park in kthread_create_on_cpu() Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 03/22] kthread: Allow to call __kthread_create_on_node() with va_list args Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 04/22] kthread: Add create_kthread_worker*() Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 18:53 ` Tejun Heo 2016-01-25 18:53 ` Tejun Heo 2016-02-16 15:44 ` Petr Mladek 2016-02-16 15:44 ` Petr Mladek 2016-02-16 16:08 ` Tejun Heo 2016-02-16 16:08 ` Tejun Heo 2016-02-16 16:08 ` Tejun Heo 2016-02-16 16:10 ` Petr Mladek 2016-02-16 16:10 ` Petr Mladek 2016-02-16 16:10 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 05/22] kthread: Add drain_kthread_worker() Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 06/22] kthread: Add destroy_kthread_worker() Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 15:44 ` Petr Mladek [this message] 2016-01-25 15:44 ` [PATCH v4 07/22] kthread: Detect when a kthread work is used by more workers Petr Mladek 2016-01-25 18:57 ` Tejun Heo 2016-01-25 18:57 ` Tejun Heo 2016-01-25 18:57 ` Tejun Heo 2016-02-16 16:38 ` Petr Mladek 2016-02-16 16:38 ` Petr Mladek 2016-02-16 16:38 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 08/22] kthread: Initial support for delayed kthread work Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 19:04 ` Tejun Heo 2016-01-25 19:04 ` Tejun Heo 2016-01-25 19:04 ` Tejun Heo 2016-01-25 15:44 ` [PATCH v4 09/22] kthread: Allow to cancel " Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 19:17 ` Tejun Heo 2016-01-25 19:17 ` Tejun Heo 2016-02-19 16:22 ` Petr Mladek 2016-02-19 16:22 ` Petr Mladek 2016-01-25 15:44 ` [PATCH v4 10/22] kthread: Allow to modify delayed " Petr Mladek 2016-01-25 15:44 ` Petr Mladek 2016-01-25 19:19 ` Tejun Heo 2016-01-25 19:19 ` Tejun Heo 2016-01-25 15:45 ` [PATCH v4 11/22] kthread: Better support freezable kthread workers Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 19:21 ` Tejun Heo 2016-01-25 19:21 ` Tejun Heo 2016-01-25 15:45 ` [PATCH v4 12/22] kthread: Use try_lock_kthread_work() in flush_kthread_work() Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 13/22] mm/huge_page: Convert khugepaged() into kthread worker API Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 14/22] ring_buffer: Convert benchmark kthreads " Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 15/22] hung_task: Convert hungtaskd " Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 16/22] kmemleak: Convert kmemleak kthread " Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 17/22] ipmi: Convert kipmi " Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 18/22] IB/fmr_pool: Convert the cleanup thread " Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 19/22] memstick/r592: Better synchronize debug messages in r592_io kthread Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 20/22] memstick/r592: convert r592_io kthread into kthread worker API Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 15:45 ` [PATCH v4 21/22] thermal/intel_powerclamp: Remove duplicated code that starts the kthread Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 16:23 ` Jacob Pan 2016-01-25 16:23 ` Jacob Pan 2016-01-25 15:45 ` [PATCH v4 22/22] thermal/intel_powerclamp: Convert the kthread to kthread worker API Petr Mladek 2016-01-25 15:45 ` Petr Mladek 2016-01-25 16:28 ` Jacob Pan 2016-01-25 16:28 ` Jacob Pan
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