** Summary changed: - Introduce and use sendpages_ok() instead of sendpage_ok() in nvme-tcp and drbg + Introduce and use sendpages_ok() instead of sendpage_ok() in nvme-tcp and drbd
** Description changed: BugLink: https://bugs.launchpad.net/bugs/2093871 [Impact] - Currently the nvme-tcp and drbg subsystems try to enable the MSG_SPLICE_PAGES + Currently the nvme-tcp and drbd subsystems try to enable the MSG_SPLICE_PAGES flag on pages to be written, and when MSG_SPLICE_PAGES is set, eventually it calls skb_splice_from_iter(), which then checks all pages with sendpage_ok() to see if all the pages are sendable. At the moment, both subsystems only check the first page in a potentially contiguous block of pages, if they are sendpage_ok(), and if the first page is, then it just assumes all the rest are sendpage_ok() too, and sends the I/O off to eventually be found out by skb_splice_from_iter(). If one or more of the pages in the contiguous block is not sendpage_ok(), then we get a warn printed, data transfer is aborted. In the nvme-tcp case, IO then hangs. This patchset introduces sendpages_ok() which iterates over each page in a contiguous block, checks if it is sendpage_ok(), and only returns true if all of them are. This resolves the whole MSG_SPLICE_PAGES flag situation, since you can now depend on the result of sendpages_ok(), instead of just assuming everything is okay. This issue is what caused bug 2075110 [0] to be discovered in the first place, since it was responsible for contigious blocks of pages where the first was sendpage_ok(), but pages further into the block were not. [0] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2075110 Even with "md/md-bitmap: fix writing non bitmap pages" applied, the issue can still happen, e.g. with merged IO pages, so this fix is still needed to eliminate the issue. [Fix] The fixes landed in mainline 6.12-rc1: commit 23a55f4492fcf868d068da31a2cd30c15f46207d Author: Ofir Gal <ofir....@volumez.com> Date: Thu Jul 18 11:45:12 2024 +0300 Subject: net: introduce helper sendpages_ok() Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=23a55f4492fcf868d068da31a2cd30c15f46207d - + commit 6af7331a70b4888df43ec1d7e1803ae2c43b6981 Author: Ofir Gal <ofir....@volumez.com> Date: Thu Jul 18 11:45:13 2024 +0300 Subject: nvme-tcp: use sendpages_ok() instead of sendpage_ok() Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6af7331a70b4888df43ec1d7e1803ae2c43b6981 - + commit 7960af373ade3b39e10106ef415e43a1d2aa48c6 Author: Ofir Gal <ofir....@volumez.com> Date: Thu Jul 18 11:45:14 2024 +0300 Subject: drbd: use sendpages_ok() instead of sendpage_ok() Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7960af373ade3b39e10106ef415e43a1d2aa48c6 They are needed for noble and oracular. [Testcase] This is the same testcase as the original bug 2075110 [0], as the fix is designed to prevent it or similar other bugs from happening again. [0] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2075110 Because of this, the fix: commit ab99a87542f194f28e2364a42afbf9fb48b1c724 Author: Ofir Gal <ofir....@volumez.com> Date: Fri Jun 7 10:27:44 2024 +0300 Subject: md/md-bitmap: fix writing non bitmap pages Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ab99a87542f194f28e2364a42afbf9fb48b1c724 needs to be reverted during your test runs, or you won't see the issue reproduce. You can use this ppa for updated kernels with the revert to trigger the issue: https://launchpad.net/~mruffell/+archive/ubuntu/sf404844-revert This can be reproduced by running blktests md/001 [1], which the author of the fix created to act as a regression test for this issue. [1] https://github.com/osandov/blktests/commit/a24a7b462816fbad7dc6c175e53fcc764ad0a822 Deploy a fresh Noble VM, that has a scratch NVME disk. $ sudo apt install build-essential fio $ git clone https://github.com/osandov/blktests.git $ cd blktests $ make $ echo "TEST_DEVS=(/dev/nvme0n1)" > config $ sudo ./check md/001 The md/001 test will hang an affected system, and the above oops message will be visible in dmesg. A test kernel is available in the following ppa: https://launchpad.net/~mruffell/+archive/ubuntu/sf404844-test This has both the fixes for this bug, and also bug 2075110. The issue will not reproduce. There is also a test kernel available with the fix for this bug present, and the fix for bug 2075110 reverted, so you can see the impact of these patches only: https://launchpad.net/~mruffell/+archive/ubuntu/sf404844-repro This will also not reproduce the issue anymore. [Where problems could occur] What we are changing is rather simple. Instead of checking the first page and assuming all the rest in the contiguous block are sendpage_ok(), we now check each page in the contiguous block to see if all of them are sendpage_ok(). If any aren't, then we abort the write to the driver, and try again later. This saves us time. However, it does take longer to call sendpage_ok() on each of the pages in the contiguous block, so there will be a minor performance hit. Small performance hit for correctness should be okay. - Currently we are only applying to nvme-tcp and drbg subsystems. If a regression + Currently we are only applying to nvme-tcp and drbd subsystems. If a regression were to occur, it would affect users of those subsystems only. [Other info] Upstream mailing list: https://lore.kernel.org/all/20240718084515.3833733-1-ofir....@volumez.com/T/#u -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2093871 Title: Introduce and use sendpages_ok() instead of sendpage_ok() in nvme-tcp and drbd To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2093871/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
