I have backported the fix from cups-browsed 2.1.1 also to the cups- browsed packages of Noble (2.0.0-0ubuntu10.3) and Oracular (2.0.1-0ubuntu2.2) and uploaded them.
As soon as these packages are accepted into the -proposed repositories, testing instructions will get posted here. Please test then and report your results here. ** Description changed: + [ Impact ] + + During the past months it often happened that a user observed that cups- + browsed takes 100% or 200% (2 cores) of CPU and ceases to do its actual + work. This even happens for users who do not print anything, just + printers shared by other computers in the local network, triggering + cups-browsed to make them available on the local machine, can make cups- + browsed getting stuck hogging 1 or 2 CPU cores. To free the CPU cores + and make cups-browsed working again one needs to kill and restart it. + + The bug is not easily reproducible. It only occurs sporadically. + Restarting a stuck cups-browsed will not end up getting it stuck + immediately again. + + It is annoying for the user that suddenly a significant part of their + CPU power gets hogged and the machine's fan producing noise. Especially + most users do not know the root cause of it and how to stop it. + + The problem is caused by concurrent use of one global HTTP connection to + CUPS by several sub-threads. This corrupts the data structure which + makes the httpGets() function of CUPS fall into an infinite loop. The + proposed packages (for Noble and Oracular) contain a backport of the fix + of the upstream version 2.1.1 (already uploaded to Plucky). This fix + lets each function create its own HTTP connection to CUPS instead of + using one single global one. None of these is used by multiple threads + and therefore the problem should go away. + + The fix I did solely do by taking a few backtraces (by reporters of the + bug and one where I observed the bug by myself) to locate it (gets + always stuck in httpGets() of libcups), and reviewing the HTTP-related + code of libcups and of cups-browsed, discovering the described problem + and remedying it as described. I did not do any before/after testing. I + only based my self on my observations and code reviews. + + What happens in httpGets() is described in my comments here (especially + near the end): + + https://github.com/OpenPrinting/cups/issues/879 + + [ Test Plan ] + + Due to the problem only occuring sporadically it is not easy to make a + test, install the proposed, fixed version, do the same test again and + see that the problem has disappeared. + + But if somebody of you observes the bug with a certain frequency, like + in 1 of 10 attempts for example, you could try until getting the bug + with the old version, update, and then try again, if you reach a + reasonably high number of tests without the bug occuring again, you + could consider it as fixed. + + The bug requires cups-browsed to create or remove local CUPS queues for + remote printers, so that it interacts with the local CUPS, which it does + by IPP, using libcups' HTTP API. This requires the appearing and + disappearing of network printers, emulations of them with tools like + ippeveprinter, or shared remote CUPS queues. Also disruption in the + network connection between a remote server (printer, CUPS) and the + client, like shutting down network connection or suspending the machine + could cause the problem. + + A possible situation where it happened but we have no proof was on a + Canonical Sprint (where all of Canonical's engineers meet physically). I + have some print queues on my laptop which are shared (and so other + people could see them in their print dialogs) and during the event I + often had to get from one room to another and for that I closed my + laptop, it suspended, and went to the other room where I opened again. + Other people on the event observed the bug. I already tried to cause it + by myself, suspending a laptop which shares printers and observing cups- + browsed on another laptop but I was not able to reproduce it. Probably + the Sprint with a big network and many people is a different situation. + + So unfortunately I am not able to force the occurrence of this bug. + + A possible way could be brute-forcing with many printers, writing a + script starting 100s of instances of ippeveprinter or so. + + To test cups-browsed without having a printer one can use cups-browsed's + own test script, test/run-tests.sh in the source code of cups-browsed. + + The test script, applying to the installed cups-browsed can be run most + easily as follows: + + $ sudo apt install cups-browsed-tests + $ mkdir test + $ cd test + $ cp /usr/share/cups-browsed-tests/* . + $ /usr/bin/run-tests.sh 3 no + + The script creates 2 printers with ippeveprinter, checks whether cups- + browsed creates queues for them, printes on one of them, checks + completion of the job, then stops the ippeveprinter instances one by one + and checks whether cups-browsed removes the queues. This is the + autopkgtest of cups-browsed. Running it manually as described I was not + able to trigger this bug, but modifying it to run 100 instances of + ippeveprinter or letting it do "kill -9" on ippeveprinter instances + could perhaps cause the bug. + + The script also serves as regression test and on cups-browsed 2.1.1 + (which contains the fix) it works as described here. Also "make check" + (uses this script, too) on the Noble and Oracular packages proposed here + passes and so does not reveal any regressions. + + So I am also asking any of the reporters of these bugs, whether they + observe the bug with enough frequency or know how to force the bug to + occur (please tell, how, then), to check whether the proposed packages + make the bug not appearing any more and tell their results here. + + [ Where problems could occur ] + + The patch is rather long and I have done only basic tests to check + whether cups-browsed is still working as designed. So there is a + regression potential. So I also ask everybody reading this, including + those who did not observe or are not able to reproduce the bug reported + here to test whether the fixed cups-browsed is still working as they + expected, or if there is some regression. + + [ Original description ] + After waking up from standby cups-browsed runs incessantly on two cores: 18243 cups-br+ 20 0 432256 26348 17848 R 99.7 0.2 66:54.73 cups-br+ 85147 cups-br+ 20 0 432256 26348 17848 R 99.7 0.2 66:52.08 cups-br+ cups-br+ 18243 18.9 0.1 432256 26348 ? Rsl 08:30 135:06 /usr/sbin/cups-browsed Best regards Heinrich ProblemType: Bug DistroRelease: Ubuntu 24.04 Package: cups-browsed 2.0.0-0ubuntu2 ProcVersionSignature: Ubuntu 6.6.0-14.14-generic 6.6.3 Uname: Linux 6.6.0-14-generic x86_64 ApportVersion: 2.27.0-0ubuntu6 Architecture: amd64 CasperMD5CheckResult: pass CurrentDesktop: KDE Date: Sun Jan 14 20:19:22 2024 InstallationDate: Installed on 2021-07-01 (927 days ago) InstallationMedia: Kubuntu 21.04 "Hirsute Hippo" - Release amd64 (20210420) MachineType: {report['dmi.sys.vendor']} {report['dmi.product.name']} Papersize: a4 ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-6.6.0-14-generic root=/dev/mapper/vgubuntu-root ro SourcePackage: cups-browsed UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 02/08/2023 dmi.bios.release: 1.63 dmi.bios.vendor: LENOVO dmi.bios.version: R0UET83W (1.63 ) dmi.board.asset.tag: Not Available dmi.board.name: 20KV0008GE dmi.board.vendor: LENOVO dmi.board.version: SDK0J40697 WIN dmi.chassis.asset.tag: No Asset Information dmi.chassis.type: 10 dmi.chassis.vendor: LENOVO dmi.chassis.version: None dmi.ec.firmware.release: 1.63 dmi.modalias: dmi:bvnLENOVO:bvrR0UET83W(1.63):bd02/08/2023:br1.63:efr1.63:svnLENOVO:pn20KV0008GE:pvrThinkPadE585:rvnLENOVO:rn20KV0008GE:rvrSDK0J40697WIN:cvnLENOVO:ct10:cvrNone:skuLENOVO_MT_20KV_BU_Think_FM_ThinkPadE585: dmi.product.family: ThinkPad E585 dmi.product.name: 20KV0008GE dmi.product.sku: LENOVO_MT_20KV_BU_Think_FM_ThinkPad E585 dmi.product.version: ThinkPad E585 dmi.sys.vendor: LENOVO ** Changed in: cups-browsed (Ubuntu Oracular) Status: New => Confirmed ** Changed in: cups-browsed (Ubuntu Noble) Status: New => Confirmed -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2049315 Title: cups-browsed running non-stop on two cores To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/cups-browsed/+bug/2049315/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
