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The e1000e driver and related hardware has a limitation on Tx PTP packets which requires we limit to timestamping a single packet at once. We do this by verifying that we never request a new Tx timestamp while we still have a tx_hwtstamp_skb pointer. Unfortunately the driver suffers from a race condition around this. The tx_hwtstamp_skb pointer is not set to NULL until after skb_tstamp_tx() is called. This function notifies the stack and applications of a new timestamp. Even a well behaved application that only sends a new request when the first one is finished might be woken up and possibly send a packet before we can free the timestamp in the driver again. The result is that we needlessly ignore some Tx timestamp requests in this corner case. Fix this by assigning the tx_hwtstamp_skb pointer prior to calling skb_tstamp_tx() and use a temporary pointer to hold the timestamped skb until that function finishes. This ensures that the application is not woken up until the driver is ready to begin timestamping a new packet. This ensures that well behaved applications do not accidentally race with condition to skip Tx timestamps. Obviously an application which sends multiple Tx timestamp requests at once will still only timestamp one packet at a time. Unfortunately there is nothing we can do about this. Reported-by: David Mirabito <davidm@metamako.com> Signed-off-by: Jacob Keller <jacob.e.keller@intel.com> Tested-by: Aaron Brown <aaron.f.brown@intel.com> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.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.