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SeongJae Park
b32f4cd81e
commit64a140afa5upstream. Patch series "mm/damon/modules: detect and use fresh status", v3. DAMON modules including DAMON_RECLAIM, DAMON_LRU_SORT and DAMON_STAT commonly expose the kdamond running status via their parameters. Under certain scenarios including wrong user inputs and memory allocation failures, those parameter values can be stale. It can confuse users. For DAMON_RECLAIM and DAMON_LRU_SORT, it even makes the kdamond unable to be restarted before the system reboot. The problem comes from the fact that there are multiple events for the status changes and it is difficult to follow up all the scenarios. Fix the issue by detecting and using the status on demand, instead of using a cached status that is difficult to be updated. Patches 1-3 fix the bugs in DAMON_RECLAIM, DAMON_LRU_SORT and DAMON_STAT in the order. This patch (of 3): DAMON_RECLAIM updates 'enabled' and 'kdamond_pid' parameter values, which represents the running status of its kdamond, when the user explicitly requests start/stop of the kdamond. The kdamond can, however, be stopped in events other than the explicit user request in the following three events. 1. ctx->regions_score_histogram allocation failure at beginning of the execution, 2. damon_commit_ctx() failure due to invalid user input, and 3. damon_commit_ctx() failure due to its internal allocation failures. Hence, if the kdamond is stopped by the above three events, the values of the status parameters can be stale. Users could show the stale values and be confused. This is already bad, but the real consequence is worse. DAMON_RECLAIM avoids unnecessary damon_start() and damon_stop() calls based on the 'enabled' parameter value. And the update of 'enabled' parameter value depends on the damon_start() and damon_stop() call results. Hence, once the kdamond has stopped by the unintentional events, the user cannot restart the kdamond before the system reboot. For example, the issue can be reproduced via below steps. # cd /sys/module/damon_reclaim/parameters # # # start DAMON_RECLAIM # echo Y > enabled # ps -ef | grep kdamond root 806 2 0 17:53 ? 00:00:00 [kdamond.0] root 808 803 0 17:53 pts/4 00:00:00 grep kdamond # # # commit wrong input to stop kdamond withou explicit stop request # echo 3 > addr_unit # echo Y > commit_inputs bash: echo: write error: Invalid argument # # # confirm kdamond is stopped # ps -ef | grep kdamond root 811 803 0 17:53 pts/4 00:00:00 grep kdamond # # # users casn now show stable status # cat enabled Y # cat kdamond_pid 806 # # # even after fixing the wrong parameter, # # kdamond cannot be restarted. # echo 1 > addr_unit # echo Y > enabled # ps -ef | grep kdamond root 815 803 0 17:54 pts/4 00:00:00 grep kdamond The problem will only rarely happen in real and common setups for the following reasons. The allocation failures are unlikely in such setups since those allocations are arguably too small to fail. Also sane users on real production environments may not commit wrong input parameters. But once it happens, the consequence is quite bad. And the bug is a bug. The issue stems from the fact that there are multiple events that can change the status, and following all the events is challenging. Dynamically detect and use the fresh status for the parameters when those are requested. Link: https://lore.kernel.org/20260419161003.79176-1-sj@kernel.org Link: https://lore.kernel.org/20260419161003.79176-2-sj@kernel.org Fixes:e035c280f6("mm/damon/reclaim: support online inputs update") Co-developed-by: Liew Rui Yan <aethernet65535@gmail.com> Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com> Signed-off-by: SeongJae Park <sj@kernel.org> Cc: <stable@vger.kernel.org> # 5.19.x Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: SeongJae Park <sj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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
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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
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