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It is not safe to have the string table for statistics change order or size over the lifetime of a given netdevice. This is because of the nature of the 3-step process for obtaining stats. First, user space performs a request for the size of the strings table. Second it performs a separate request for the strings themselves, after allocating space for the table. Third, it requests the stats themselves, also allocating space for the table. If the size decreased, there is potential to see garbage data or stats values. In the worst case, we could potentially see stats values become mis-aligned with their strings, so that it looks like a statistic is being reported differently than it actually is. Even worse, if the size increased, there is potential that the strings table or stats table was not allocated large enough and the stats code could access and write to memory it should not, potentially resulting in undefined behavior and system crashes. It isn't even safe if the size always changes under the RTNL lock. This is because the calls take place over multiple user space commands, so it is not possible to hold the RTNL lock for the entire duration of obtaining strings and stats. Further, not all consumers of the ethtool API are the user space ethtool program, and it is possible that one assumes the strings will not change (valid under the current contract), and thus only requests the stats values when requesting stats in a loop. Finally, it's not possible in the general case to detect when the size changes, because it is quite possible that one value which could impact the stat size increased, while another decreased. This would result in the same total number of stats, but reordering them so that stats no longer line up with the strings they belong to. Since only size changes aren't enough, we would need some sort of hash or token to determine when the strings no longer match. This would require extending the ethtool stats commands, but there is no more space in the relevant structures. The real solution to resolve this would be to add a completely new API for stats, probably over netlink. In the ice driver, the only thing impacting the stats that is not constant is the number of queues. Instead of reporting stats for each used queue, report stats for each allocated queue. We do not change the number of queues allocated for a given netdevice, as we pass this into the alloc_etherdev_mq() function to set the num_tx_queues and num_rx_queues. This resolves the potential bugs at the slight cost of displaying many queue statistics which will not be activated. Signed-off-by: Jacob Keller <jacob.e.keller@intel.com> Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com> Tested-by: Tony Brelinski <tonyx.brelinski@intel.com> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com> |
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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.
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.