Messages in this thread | | | Subject | Re: [PATCH v12 15/17] counter: Implement events_queue_size sysfs attribute | From | David Lechner <> | Date | Sat, 10 Jul 2021 12:53:54 -0500 |
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On 7/10/21 11:08 AM, David Lechner wrote: > On 7/10/21 10:43 AM, David Lechner wrote: >> On 7/10/21 5:25 AM, William Breathitt Gray wrote: >>>> and after that >>>> >>>> [ 16.564403] ================================================ >>>> [ 16.570725] WARNING: lock held when returning to user space! >>>> [ 16.577044] 5.13.0-next-20210706+ #4 Not tainted >>>> [ 16.582198] ------------------------------------------------ >>>> [ 16.588507] cat/331 is leaving the kernel with locks still held! >>>> [ 16.595214] 1 lock held by cat/331: >>>> [ 16.599103] #0: ffff888102bb3630 >>>> (&counter->chrdev_lock){+.+.}-{3:3}, at: counter_chrdev_open+0x21/0x60 >>>> [counter] >>>> >>>> Jarkko >>> I'm not sure how to resolve this warning. The purpose of this lock is to >>> limit chrdev to a single open at a time. To accomplish this I grab this >>> lock in counter_chrdev_open() and hold it until counter_chrdev_release() >>> is called. Is there a better way to accomplish this? >> >> How about using an atomic flag, e.g test_and_set_bit()? > > Another option could be to rethink it at a higher level and avoid the > need for a lock (and sysfs attribute) altogether. For example, would it > work to (re)allocate the kfifo buffer in the COUNTER_ENABLE_EVENTS_IOCTL > callback and add a parameter to that ioctl to specify the buffer size > (with units of events rather than bytes)? >
Thinking about it a bit more, this probably isn't a good suggestion. It would create issues with being able to start reading from the chrdev before enabling events.
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