Messages in this thread | | | From | John Ogness <> | Subject | Re: synchronization model: was: Re: [PATCH printk-rework 09/14] printk: introduce a kmsg_dump iterator | Date | Wed, 24 Feb 2021 16:40:24 +0100 |
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On 2021-02-24, John Ogness <john.ogness@linutronix.de> wrote: > The @active flag is useless. It should be removed.
I would like to clarify my statement, because the @active flag _did_ protect the arch/um dumper until now. (Although it didn't actually matter because arch/um does not have SMP or preemption support.)
In mainline we have 6 dumpers. They can be classified as follows:
1. Dumpers that provide their own synchronization to protect against parallel or nested dump() calls.
- arch/powerpc/kernel/nvram_64.c - fs/pstore/platform.c - arch/um/kernel/kmsg_dump.c (after this series)
2. Dumpers that are safe because they only dump on KMSG_DUMP_PANIC, which (currently) can never happen in parallel or nested.
- arch/powerpc/platforms/powernv/opal-kmsg.c - drivers/hv/vmbus_drv.c
3. Dumpers that are unsafe and even @active did not provide the needed synchronization.
- drivers/mtd/mtdoops.c
In all 6 dumpers, @action does not provide any help. That is why it can be removed.
But I am concerned about drivers/mtd/mtdoops.c that does not have any synchronization. Since my series is adding sychronization to arch/um/kernel/kmsg_dump.c, I suppose it should also add it to drivers/mtd/mtdoops.c also.
And rather than moving the useless @active from kmsg_dumper to kmsg_dump_iter, I should just drop it.
Unless there are any objections, I will make these changes for my v3.
John Ogness
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