Messages in this thread | | | Date | Thu, 12 May 2022 20:32:10 +0900 | Subject | Re: [PATCH v3 (repost)] workqueue: Warn flushing of kernel-global workqueues | From | Tetsuo Handa <> |
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On 2022/05/12 19:38, Dmitry Torokhov wrote: > Hi Tejun, > > On Mon, Mar 21, 2022 at 07:02:45AM -1000, Tejun Heo wrote: >> I'm willing to bet that the majority of the use cases can be converted to >> use flush_work() and that'd be the preference. We need a separate workqueue >> iff the flush requrement is complex (e.g. there are multiple dynamic work >> items in flight which need to be flushed together) or the work items needs >> some special attributes (such as MEM_RECLAIM or HIGHPRI) which don't apply >> to the system_wq users in the first place. > > This means that now the code has to keep track of all work items that it > allocated, instead of being able "fire and forget" works (when dealing > with extremely infrequent events) and rely on flush_workqueue() to > cleanup.
Yes. Moreover, a patch to catch and refuse at compile time was proposed at https://lkml.kernel.org/r/738afe71-2983-05d5-f0fc-d94efbdf7634@I-love.SAKURA.ne.jp .
> That flush typically happens in module unload path, and I > wonder if the restriction on flush_workqueue() could be relaxed to allow > calling it on unload.
A patch for drivers/input/mouse/psmouse-smbus.c is waiting for your response at https://lkml.kernel.org/r/25e2b787-cb2c-fb0d-d62c-6577ad1cd9df@I-love.SAKURA.ne.jp . Like many modules, flush_workqueue() happens on only module unload in your case.
We currently don't have a flag to tell whether the caller is inside module unload path. And even inside module unload path, flushing the system-wide workqueue is problematic under e.g. GFP_NOFS/GFP_NOIO context. Therefore, I don't think that the caller is inside module unload path as a good exception.
Removing flush_scheduled_work() is for proactively avoiding new problems like https://lkml.kernel.org/r/385ce718-f965-4005-56b6-34922c4533b8@I-love.SAKURA.ne.jp and https://lkml.kernel.org/r/20220225112405.355599-10-Jerome.Pouiller@silabs.com .
Using local WQ also helps for documentation purpose. This change makes clear where the work's dependency is. Please grep the linux-next.git tree. Some have been already converted.
Any chance you have too many out-of-tree modules to convert?
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