Piping commands that use PCBUF sometimes hang

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This is related to the fact that one command (e.g. PS) uses PCBUF to get information from the kernel, tries, to write it to STDOUT, so it locks PCBUF during this time, while the shell still tries to open the down-pipe process, which is also using PCBUF to open the file and FORK.

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What could be a possible solution?

• the shell keeps locking PCBUF as long as it is needed to build the complete pipe chain. This is similar to what init and filesystems do today, init locks PCBUF with PSEM and the filesystem releases once it has registered itself with VSEM. But forked processes now "inherit" the semaphore, and release it - should FORK provide some block that too?
• PS needs to copy away the data and immediately release PCBUF

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Fixed