kernel/git/next/linux-next.git/samples/damon, branch master

samples/damon/prcl: do not stop DAMON for damon_call() failure

2026-07-10T03:15:34+00:00

damon_call() failure was causing the context to be stopped, but asynchronously by the kdamond thread. To handle the race, the caller had to stop the context. damon_call() is updated to do the stop on its own. Remove the damon_stop() call from the damon_call() error handling. Link: https://lore.kernel.org/20260706140628.87414-12-sj@kernel.org Signed-off-by: SJ Park Signed-off-by: Andrew Morton

samples/damon/wsse: do not stop ctx for damon_call() failure

2026-07-10T03:15:34+00:00

damon_call() failure was causing the context to be stopped, but asynchronously by the kdamond thread. To handle the race, the caller had to stop the context. damon_call() is updated to do the stop on its own. Remove the damon_stop() call from the damon_call() error handling. Link: https://lore.kernel.org/20260706140628.87414-11-sj@kernel.org Signed-off-by: SJ Park Signed-off-by: Andrew Morton

samples/damon/mtier: stop all contexts with single damon_stop() call

2026-07-10T03:15:34+00:00

damon_stop() was theoretically able to return failure while keeping the second context for mtier running. mtier stops its contexts one by one with two damon_stop() call for the reason. damon_stop() is refactored to always successfully stop all requested DAMON contexts. The two calls are unnecessary. Use only single damon_stop() call for all contexts. Link: https://lore.kernel.org/20260706140628.87414-9-sj@kernel.org Signed-off-by: SJ Park Signed-off-by: Andrew Morton

samples/damon/mtier: do not stop first context for damon_start() failure

2026-07-10T03:15:32+00:00

damon_start() was able to fail while keeping the first context running. mtier hence stops the first context in the case. damon_start() is refactored to avoid that. The error handling is no longer necessary. Remove it. Link: https://lore.kernel.org/20260706140628.87414-3-sj@kernel.org Signed-off-by: SJ Park Signed-off-by: Andrew Morton

samples/damon: fix typos in Kconfig help text

2026-07-10T03:14:55+00:00

Fix a couple of typos in samples/damon/Kconfig help text. Change "Thps" to "This", and "tierign" to "tiering". Link: https://lore.kernel.org/20260629145538.134832-5-sj@kernel.org Signed-off-by: Asier Gutierrez Signed-off-by: SJ Park Reviewed-by: SJ Park Cc: Akinobu Mita Cc: Brendan Higgins Cc: David Hildenbrand Cc: Doehyun Baek Cc: Jonathan Corbet Cc: "Liam R. Howlett" Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Philippe Laferriere Cc: Sailesh Nandanavanam Cc: Shuah Khan Cc: SJ Park Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton

samples/damon/prcl: stop and free damon ctx when damon_call() fails

2026-07-10T03:14:48+00:00

damon_sample_prcl_start() calls damon_call() right after damon_start() is succeeded. The kdamond that has started by the damon_start() could be terminated by itself before or in the middle of the damon_call() execution. There could be multiple reasons for such a stop including monitoring target process termination and kdamond_fn() internal memory allocation failures. In the case, damon_call() will fail and return an error without cleaning up the DAMON context object. The damon_sample_prcl_start() caller assumes it would clean up the object, though. When the user requests to start DAMON again, damon_sample_prcl_start() is called again, allocates a new DAMON context object and overwrites the pointer for the previous object. As a result, the previous context object is leaked. Safely stop the kdamond and deallocate the context object when the failure is returned. Note that the kdamond should be stopped first, because damon_call() failure means not complete termination of the kdamond but only the fact that the termination process has started. The user impact shouldn't be that significant because the race is not easy to happen, and only up to one DAMON context object can be leaked per race. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260628215447.96166-7-sj@kernel.org Link: https://lore.kernel.org/20260610035214.4850-1-sj@kernel.org [1] Fixes: a6c33f1054e3 ("samples/damon/prcl: use damon_call() repeat mode instead of damon_callback") Signed-off-by: SJ Park Reviewed-by: Zenghui Yu Cc: # 6.17.x Signed-off-by: Andrew Morton

samples/damon/wsse: stop and free damon ctx when damon_call() fails

2026-07-10T03:14:48+00:00

damon_sample_wsse_start() calls damon_call() right after damon_start() is succeeded. The kdamond that has started by the damon_start() could be terminated by itself before or in the middle of the damon_call() execution. There could be multiple reasons for such a stop including monitoring target process termination and kdamond_fn() internal memory allocation failures. In the case, damon_call() will fail and return an error without cleaning up the DAMON context object. The damon_sample_wsse_start() caller assumes it would clean up the object, though. When the user requests to start DAMON again, damon_sample_wsse_start() is called again, allocates a new DAMON context object and overwrites the pointer for the previous object. As a result, the previous context object is leaked. Safely stop the kdamond and deallocate the context object when the failure is returned. Note that the kdamond should be stopped first, because damon_call() failure means not complete termination of the kdamond but only the fact that the termination process has started. The user impact shouldn't be that significant because the race is not easy to happen, and only up to one DAMON context object can be leaked per race. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260628215447.96166-6-sj@kernel.org Link: https://lore.kernel.org/20260610034828.4632-1-sj@kernel.org [1] Fixes: cc9c1b8c205b ("samples/damon/wsse: use damon_call() repeat mode instead of damon_callback") Signed-off-by: SJ Park Reviewed-by: Zenghui Yu Cc: # 6.17.x Signed-off-by: Andrew Morton

samples/damon/mtier: handle damon_stop() failure

2026-07-10T03:14:48+00:00

damon_sample_mtier_stop() assumes its damon_stop() call will always successfully stops the two DAMON contexts. Hence it deallocates the two DAMON contexts after the damon_stop() call. However, if a given context is already stopped, damon_stop() fails and returns an error while letting the DAMON contexts that have not yet stopped keep running. This kind of unexpected early DAMON context stops could happen due to memory allocation failures in kdamond_fn(). Because damon_sample_mtier_stop() just deallocates all DAMON contexts with damon_target and damon_region objects that are linked to the contexts, the execution of the unstopped DAMON context (kdamond) ends up using the memory that freed (use-after-free). Fix the issue by separating the damon_stop() to be invoked per context. Note that DAMON_SYSFS also allows multiple DAMON contexts execution. But, it calls damon_stop() for each context one by one. Hence this issue is only in mtier. For the long term, it would be better to refactor damon_stop() to always ensure stopping all contexts regardless of the failures in the middle. Make this fix in the current way, though, to keep it simple and easy to backport. I will do the refactoring later. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260628215447.96166-5-sj@kernel.org Link: https://lore.kernel.org/20260609014219.3013-1-sj@kernel.org [1] Fixes: 82a08bde3cf7 ("samples/damon: implement a DAMON module for memory tiering") Signed-off-by: SJ Park Reviewed-by: Zenghui Yu Cc: # 6.16.x Signed-off-by: Andrew Morton

samples/damon/mtier: handle damon_start() failure

2026-07-10T03:14:47+00:00

damon_sample_mtier_start() callers assume it will clean up resources when it fails. And the function does the cleanup for context buildup failures. However, it is not doing the cleanup for damon_start() failure. As a result, when damon_start() fails, it could leak the memory for DAMON context. Also, if damon_start() fails for only the second context, the first context will indefinitely run, and avoid starting other DAMON contexts since it is running in the exclusive mode. Stop possibly started DAMON context and free the contexts in case of the failure to fix the issues. Note that the issue can reliably be reproduced because the module calls damon_start() in the exclusive mode. For example, $ sudo damo start $ echo Y | sudo tee /sys/module/damon_sample_mtier/parameters/enabled $ sudo cat /proc/allocinfo | grep damon_new_ctx Because the first command is running another DAMON instance, the second command fails the damon_start() call because the new DAMON instance cannot exclusively run. And without this fix, by repeating the second and the third commands above, we can show the memory consumption is only increasing due to the leaks. It requires the sudo permission though. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260628215447.96166-4-sj@kernel.org Link: https://lore.kernel.org/20260608112455.274231F00893@smtp.kernel.org [1] Fixes: 82a08bde3cf7 ("samples/damon: implement a DAMON module for memory tiering") Signed-off-by: SJ Park Reviewed-by: Zenghui Yu Cc: # 6.16.x Signed-off-by: Andrew Morton

samples/damon/prcl: handle damon_start() failure

2026-07-10T03:14:47+00:00

damon_sample_prcl_start() callers assume it will clean up resources when it fails. And the function does the cleanup for context buildup failures. However, it is not doing the cleanup for damon_start() failure. As a result, when damon_start() fails, it leaks the memory for DAMON context. Free the context in case of the failure to fix the issues. Note that the issue can reliably be reproduced because the module calls damon_start() in the exclusive mode. For example, $ sudo damo start $ echo $$ | sudo tee /sys/module/damon_sample_prcl/parameters/target_pid $ echo Y | sudo tee /sys/module/damon_sample_prcl/parameters/enabled $ sudo cat /proc/allocinfo | grep damon_new_ctx Because the first command is running another DAMON instance, the third command fails the damon_start() call because the new DAMON instance cannot exclusively run. And without this fix, by repeating the third and the fourth commands above, we can show the memory consumption is only increasing due to the leaks. It requires the sudo permission though. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260628215447.96166-3-sj@kernel.org Link: https://lore.kernel.org/20260609145814.70163-1-sj@kernel.org [1] Fixes: 2aca254620a8 ("samples/damon: introduce a skeleton of a smaple DAMON module for proactive reclamation") Signed-off-by: SJ Park Reviewed-by: Zenghui Yu Cc: # 6.14.x Signed-off-by: Andrew Morton