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napi_synchronize() from enetc_stop() waits until the softirq has finished execution and no longer wants to be rescheduled. However under high traffic load, this will never happen, and the interface can never be closed. The problem is the fact that the NAPI poll routine is written to update the consumer index which makes the device want to put more buffers in the RX ring, which restarts the madness again. Browsing around, it seems that some drivers like i40e keep a bit (__I40E_VSI_DOWN) which they use as communication between the control path and the data path. But that isn't my first choice, because complications ensue - since the enetc hardirq may trigger while we are in a theoretical ENETC_DOWN state, it may happen that enetc_msix() masks it, but enetc_poll() never unmasks it. To prevent a stall in that case, one would need to schedule all NAPI instances when ENETC_DOWN gets cleared, to process what's pending. I find it more desirable for the control path - enetc_stop() - to just quiesce the RX ring and let the softirq finish what remains there, without any explicit communication, just by making hardware not provide any more packets. This seems possible with the Enable bit of the RX BD ring (RBaMR[EN]). I can't seem to find an exact definition of what this bit does, but when the RX ring is disabled, the port seems to no longer update the producer index, and not react to software updates of the consumer index. In fact, the RBaMR[EN] bit is already toggled by the driver, but too late for what we want: enetc_close() -> enetc_stop() -> napi_synchronize() -> enetc_clear_bdrs() -> enetc_clear_rxbdr() The enetc_clear_bdrs() function contains not only logic to disable the RX and TX rings, but also logic to wait for the TX ring stop being busy. We split enetc_clear_bdrs() into enetc_disable_bdrs() and enetc_wait_bdrs(). One needs to run before napi_synchronize() and the other after (NAPI also processes TX completions, so we maximize our chances of not waiting for the ENETC_TBSR_BUSY bit - unless a packet is stuck for some reason, ofc). We also split off enetc_enable_bdrs() from enetc_setup_bdrs(), and call this from the mirror position in enetc_start() compared to enetc_stop(), i.e. right before netif_tx_start_all_queues(). Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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| drivers | ||
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| init | ||
| io_uring | ||
| ipc | ||
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| lib | ||
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| .clang-format | ||
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.