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Thu, 26 Jun 2025 04:59:33 -0400 (EDT) Message-ID: <7069cc77-a224-4753-8088-0302fc444710@pobox.com> Date: Thu, 26 Jun 2025 01:59:32 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6.15 000/588] 6.15.4-rc2 review From: "Barry K. Nathan" To: =?UTF-8?Q?Holger_Hoffst=C3=A4tte?= , Greg Kroah-Hartman Cc: stable@vger.kernel.org, patches@lists.linux.dev, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, linux@roeck-us.net, shuah@kernel.org, patches@kernelci.org, lkft-triage@lists.linaro.org, pavel@denx.de, jonathanh@nvidia.com, f.fainelli@gmail.com, sudipm.mukherjee@gmail.com, srw@sladewatkins.net, rwarsow@gmx.de, conor@kernel.org, hargar@microsoft.com, broonie@kernel.org, Christian Brauner References: <20250624121449.136416081@linuxfoundation.org> <2025062511-tutor-judiciary-e3f9@gregkh> <6d3b0f28-98cb-46dd-b971-8a11e3b69d68@pobox.com> Content-Language: en-US In-Reply-To: <6d3b0f28-98cb-46dd-b971-8a11e3b69d68@pobox.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 6/25/25 05:15, Barry K. Nathan wrote: > On 6/25/25 02:08, Holger Hoffstätte wrote: >> On 2025-06-25 10:25, Greg Kroah-Hartman wrote: >>> On Wed, Jun 25, 2025 at 10:00:56AM +0200, Holger Hoffstätte wrote: >>>> (cc: Christian Brauner> >>>> >>>> Since 6.15.4-rc1 I noticed that some KDE apps (kded6, kate (the text >>>> editor)) >>>> started going into a tailspin with 100% per-process CPU. >>>> >>>> The symptom is 100% reproducible: open a new file with kate, save >>>> empty file, >>>> make changes, save, watch CPU go 100%. perf top shows copy_to_user >>>> running wild. >>>> >>>> First I tried to reproduce on 6.15.3 - no problem, everything works >>>> fine. >>>> >>>> After checking the list of patches for 6.15.4 I reverted the >>>> anon_inode series >>>> (all 3 for the first attempt) and the problem is gone. >>>> >>>> Will try to reduce further & can gladly try additional fixes, but >>>> for now >>>> I'd say these patches are not yet suitable for stable. >>> >>> Does this same issue also happen for you on 6.16-rc3? >> >> Curiously it does *not* happen on 6.16-rc3, so that's good. >> I edited/saved several files and everything works as it should. >> >> In 6.15.4-rc the problem occurs (as suspected) with: >> anon_inode-use-a-proper-mode-internally.patch aka cfd86ef7e8e7 upstream. >> >> thanks >> Holger > > For what it's worth, I can confirm this reproduces easily and > consistently on Debian trixie's KDE (6.3.5), with either Wayland or X11. > It reproduces with kernel 6.15.4-rc2, and with 6.15.3+anon_inode-use-a- > proper-mode-internally.patch, but not with vanilla 6.15.3 or with 6.16-rc3. > > By the way, my test VM has both GNOME and KDE installed. If I boot one > of the affected kernels and log into a GNOME session, I don't get any > GNOME processes chewing up CPU the way that some of the KDE processes > do. However, if I then start kate within the GNOME session and follow > the steps to reproduce (create a new file, save it immediately, type a > few characters, save again), kate still starts using 100% CPU. After some testing and bisecting, I found that "anon_inode: use a proper mode internally" needs to be followed up with "fs: add S_ANON_INODE" (upstream commit 19bbfe7b5fcc) in order to avoid this regression. -- -Barry K. Nathan