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At queue creation, the transport allocates a local job struct (struct nvmet_fc_fcp_iod) for each possible element of the queue. When a new CMD is received from the wire, a jobs struct is allocated from the queue and then used for the duration of the command. The job struct contains buffer space for the wire command iu. Thus, upon allocation of the job struct, the cmd iu buffer is copied to the job struct and the LLDD may immediately free/reuse the CMD IU buffer passed in the call. However, in some circumstances, due to the packetized nature of FC and the api of the FC LLDD which may issue a hw command to send the wire response, but the LLDD may not get the hw completion for the command and upcall the nvmet_fc layer before a new command may be asynchronously received on the wire. In other words, its possible for the initiator to get the response from the wire, thus believe a command slot free, and send a new command iu. The new command iu may be received by the LLDD and passed to the transport before the LLDD had serviced the hw completion and made the teardown calls for the original job struct. As such, there is no available job struct available for the new io. E.g. it appears like the host sent more queue elements than the queue size. It didn't based on it's understanding. Rather than treat this as a hard connection failure queue the new request until the job struct does free up. As the buffer isn't copied as there's no job struct, a special return value must be returned to the LLDD to signify to hold off on recycling the cmd iu buffer. And later, when a job struct is allocated and the buffer copied, a new LLDD callback is introduced to notify the LLDD and allow it to recycle it's command iu buffer. Signed-off-by: James Smart <james.smart@broadcom.com> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> Signed-off-by: Christoph Hellwig <hch@lst.de> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.