Date: Wed, 04 Mar 2026 18:39:40 +0000 From: Unitrunker <unitrunker@unitrunker.net> To: Christos Margiolis <christos@freebsd.org> Cc: freebsd-multimedia@freebsd.org Subject: Re: cuse(3) cuse_wait_and_process thread safety Message-ID: <O6xsN77qp2qbzGLHJ2sk9zJjv2_9c45cEpB4JPv3enS-tCdka9dyy87RDvYZ7siuGQkNzuH6JG6TpSZ2XQ0yj6m2Cx4v7TI1Emkd6cHijRQ=@unitrunker.net> In-Reply-To: <DGU7BRMO0NSM.1R59RB18HVL88@freebsd.org> References: <z4gb0FHta2RgVVOgb9R1aetw5B-mIlUajdokq7xGi4thxQVtsIcZkCTsL4o6WzZbgwx4qy6b4LQoc_mulgDaiPV2BvRL08z-tW-eZLipmdc=@unitrunker.net> <DGU7BRMO0NSM.1R59RB18HVL88@freebsd.org>
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Hello Christos! I am working on a POC to demonstrate the problem. While doing so I found a separate issue with readv. Bug is here: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=293489 Multiple threads make sense but one would want to partition the data so that packets inside the same stream are processed in-order. My theory of a bug is based on two assumptions. I am assuming the kernel module does not enforce one-stream per worker thread (which may be wrong but I've not seen such logic in the module). For the POC, I created a simple cuse process and a test program that sends a burst of one byte writes to the cuse process. Inside the cuse process, each worker thread sleeps a random amount of time in between events. This requires multiple events to be queued (which I assume is possible). Another process reads the data. Any mis-ordering of bytes is proof of a bug. Example: ABCDEFGH => ABCEDFGH I'll drop a POC once I have it working. Of course, if I can't make it fail, that's a good thing. Regards, Rick On Wednesday, March 4th, 2026 at 12:16 PM, Christos Margiolis <christos@freebsd.org> wrote: > I'm the maintainer of virtual_oss. To be fair, I don't know what was > HPS's (RIP) rationale for giving each device 4 threads, so I'm not sure > how to answer this question. Have you run into the problem you described > since you sent the email? > > Christoshome | help
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