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![]() Ben Coddington has noted the following race between OPEN and CLOSE on a single client. Process 1 Process 2 Server ========= ========= ====== 1) OPEN file 2) OPEN file 3) Process OPEN (1) seqid=1 4) Process OPEN (2) seqid=2 5) Reply OPEN (2) 6) Receive reply (2) 7) new stateid, seqid=2 8) CLOSE file, using stateid w/ seqid=2 9) Reply OPEN (1) 10( Process CLOSE (8) 11) Reply CLOSE (8) 12) Forget stateid file closed 13) Receive reply (7) 14) Forget stateid file closed. 15) Receive reply (1). 16) New stateid seqid=1 is really the same stateid that was closed. IOW: the reply to the first OPEN is delayed. Since "Process 2" does not wait before closing the file, and it does not cache the closed stateid, then when the delayed reply is finally received, it is treated as setting up a new stateid by the client. The fix is to ensure that the client processes the OPEN and CLOSE calls in the same order in which the server processed them. This commit ensures that we examine the seqid of the stateid returned by OPEN. If it is a new stateid, we assume the seqid must be equal to the value 1, and that each state transition increments the seqid value by 1 (See RFC7530, Section 9.1.4.2, and RFC5661, Section 8.2.2). If the tracker sees that an OPEN returns with a seqid that is greater than the cached seqid + 1, then it bumps a flag to ensure that the caller waits for the RPCs carrying the missing seqids to complete. Note that there can still be pathologies where the server crashes before it can even send us the missing seqids. Since the OPEN call is still holding a slot when it waits here, that could cause the recovery to stall forever. To avoid that, we time out after a 5 second wait. Reported-by: Benjamin Coddington <bcodding@redhat.com> Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com> |
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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.