kernel/linux.git/mm, branch v6.1.179

mm: refactor mm_access() to not return NULL

2026-07-29T15:47:48+00:00

[ Upstream commit cd3f8467afd470ccab0de2fbc7c76664af4a0bac ] mm_access() can return NULL if the mm is not found, but this is handled the same as an error in all callers, with some translating this into an -ESRCH error. Only proc_mem_open() returns NULL if no mm is found, however in this case it is clearer and makes more sense to explicitly handle the error. Additionally we take the opportunity to refactor the function to eliminate unnecessary nesting. Simplify things by simply returning -ESRCH if no mm is found - this both eliminates confusing use of the IS_ERR_OR_NULL() macro, and simplifies callers which would return -ESRCH by returning this error directly. [lorenzo.stoakes@oracle.com: prefer neater pointer error comparison] Link: https://lkml.kernel.org/r/2fae1834-749a-45e1-8594-5e5979cf7103@lucifer.local Link: https://lkml.kernel.org/r/20240924201023.193135-1-lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes Suggested-by: Arnd Bergmann Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin

mm/damon/sysfs-schemes: fix dir put orders in access_pattern_add_dirs()

2026-07-24T13:55:18+00:00

commit d58fdbe37a829fd2e5803dd4e5a72992dd8c5368 upstream. Patch series "mm/damon/sysfs-schemes: fix wrong directories put orders in error paths". Error paths of damon_sysfs_access_pattern_add_dirs() and damon_sysfs_scheme_add_dirs() functions put references to directories in wrong orders. As a result, uninitialized memory dereference and/or memory leak can happen. Fix those. This patch (of 2): In access_pattern_add_dirs(), error handling path puts references starting from setup failed directories. If the failure happpened from the initial allication in the setup functions, uninitialized memory dereference happen. The allocation failures will not commonly happen, but the consequence is quite bad. Fix the wrong reference put orders. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260618005650.83868-2-sj@kernel.org Link: https://lore.kernel.org/20260617060005.86852-1-sj@kernel.org [1] Fixes: 7e84b1f8212a ("mm/damon/sysfs: support DAMON-based Operation Schemes") Signed-off-by: SeongJae Park Cc: # 5.18.x Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

mm/damon/core: make charge_addr_from aware of end-address exclusivity

2026-07-24T13:55:17+00:00

commit 5a2d162e22bf33eb89d53e802d0fc1ec422e19b6 upstream. DAMON region end address is exclusive one, but charge_addr_from is assigned assuming the end address is inclusive. As a result, DAMOS action to next up to min_region_sz memory can be skipped. This is quite negligible user impact. But, the bug is a bug that can be very simply fixed. Fix the wrong assignment to respect the exclusiveness of the address. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260428042942.118230-1-sj@kernel.org Link: https://lore.kernel.org/20260428032324.115663-1-sj@kernel.org [1] Fixes: 50585192bc2e ("mm/damon/schemes: skip already charged targets and regions") Signed-off-by: SeongJae Park Cc: # 5.16.x Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

writeback: Avoid contention on wb->list_lock when switching inodes

2026-07-24T13:55:15+00:00

[ Upstream commit e1b849cfa6b61f1c866a908c9e8dd9b5aaab820b ] There can be multiple inode switch works that are trying to switch inodes to / from the same wb. This can happen in particular if some cgroup exits which owns many (thousands) inodes and we need to switch them all. In this case several inode_switch_wbs_work_fn() instances will be just spinning on the same wb->list_lock while only one of them makes forward progress. This wastes CPU cycles and quickly leads to softlockup reports and unusable system. Instead of running several inode_switch_wbs_work_fn() instances in parallel switching to the same wb and contending on wb->list_lock, run just one work item per wb and manage a queue of isw items switching to this wb. Acked-by: Tejun Heo Signed-off-by: Jan Kara Stable-dep-of: cba38ec4cbd3 ("writeback: fix race between cgroup_writeback_umount() and inode_switch_wbs()") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mm: shrinker: fix NULL pointer dereference in debugfs

2026-07-24T13:55:14+00:00

[ Upstream commit e30453c61e185e914fde83c650e268067b140218 ] shrinker_debugfs_add() creates both "count" and "scan" debugfs files unconditionally. That assumes every shrinker implements both count_objects() and scan_objects(), which is not guaranteed. For example, the xen-backend shrinker sets count_objects() but leaves scan_objects() NULL, so writing to its scan file calls through a NULL function pointer and panics the kernel: BUG: kernel NULL pointer dereference, address: 0000000000000000 RIP: 0010:0x0 Code: Unable to access opcode bytes at 0xffffffffffffffd6. Call Trace: shrinker_debugfs_scan_write+0x12e/0x270 full_proxy_write+0x5f/0x90 vfs_write+0xde/0x420 ? filp_flush+0x75/0x90 ? filp_close+0x1d/0x30 ? do_dup2+0xb8/0x120 ksys_write+0x68/0xf0 ? filp_flush+0x75/0x90 do_syscall_64+0xb3/0x5b0 entry_SYSCALL_64_after_hwframe+0x76/0x7e The count path has the same issue in principle if a shrinker omits count_objects(). To fix it, only create "count" and "scan" debugfs files when the corresponding callbacks are present. Link: https://lore.kernel.org/20260617090052.27325-1-qi.zheng@linux.dev Fixes: bbf535fd6f06 ("mm: shrinkers: add scan interface for shrinker debugfs") Signed-off-by: Qi Zheng Reviewed-by: Muchun Song Cc: Dave Chinner Cc: Qi Zheng Cc: Roman Gushchin Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mm: shrinkers: fix debugfs file permissions

2026-07-24T13:55:13+00:00

[ Upstream commit 2124f79de6a909630d1a62b01ecc32db9f967181 ] The permissions for the files here are swapped as "count" is read-only and "scan" is write-only. While this doesn't really matter as these permissions don't stop the files being opened for reading/writing as appropriate, they are shown by "ls -l" and are confusing. Link: https://lkml.kernel.org/r/20230418101906.3131303-1-john@metanate.com Signed-off-by: John Keeping Signed-off-by: Andrew Morton Stable-dep-of: e30453c61e18 ("mm: shrinker: fix NULL pointer dereference in debugfs") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show()

2026-07-24T13:55:13+00:00

[ Upstream commit b902890c62d200b3509cb5e09cf1e0a66553c128 ] Reading the debugfs "count" file of a memcg-aware shrinker can sleep inside an RCU read-side critical section: BUG: sleeping function called from invalid context at kernel/cgroup/rstat.c:421 RCU nest depth: 1, expected: 0 css_rstat_flush mem_cgroup_flush_stats zswap_shrinker_count shrinker_debugfs_count_show shrinker_debugfs_count_show() invokes the ->count_objects() callback under rcu_read_lock(). The zswap callback flushes memcg stats via css_rstat_flush(), which may sleep, so it must not run under RCU. The RCU lock is not needed here. mem_cgroup_iter() takes RCU internally and returns a memcg holding a css reference (dropped on the next iteration or by mem_cgroup_iter_break()), so the memcg stays alive without it. The shrinker is kept alive by the open debugfs file: shrinker_free() removes the debugfs entries via debugfs_remove_recursive(), which waits for in-flight readers to drain, before call_rcu(..., shrinker_free_rcu_cb). The sibling "scan" handler already invokes the sleeping ->scan_objects() callback with no RCU section. Drop the rcu_read_lock()/rcu_read_unlock(). Link: https://lore.kernel.org/20260610232048.62930-1-shakeel.butt@linux.dev Fixes: 5035ebc644ae ("mm: shrinkers: introduce debugfs interface for memory shrinkers") Signed-off-by: Shakeel Butt Reported-by: Zenghui Yu Closes: https://lore.kernel.org/all/c052a064-cddb-494f-a0d8-f8a10b4b1c4d@linux.dev/ Suggested-by: Nhat Pham Reviewed-by: SeongJae Park Reviewed-by: Qi Zheng Tested-by: Zenghui Yu (Huawei) Reviewed-by: Nhat Pham Acked-by: Muchun Song Reviewed-by: Roman Gushchin Cc: Dave Chinner Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mm: shrinker: remove redundant shrinker_rwsem in debugfs operations

2026-07-24T13:55:13+00:00

[ Upstream commit 1dd49e58f966b1eecd935dc28458a8369ae94ad1 ] debugfs_remove_recursive() will wait for debugfs_file_put() to return, so the shrinker will not be freed when doing debugfs operations (such as shrinker_debugfs_count_show() and shrinker_debugfs_scan_write()), so there is no need to hold shrinker_rwsem during debugfs operations. Link: https://lkml.kernel.org/r/20230911092517.64141-4-zhengqi.arch@bytedance.com Signed-off-by: Qi Zheng Reviewed-by: Muchun Song Cc: Christian Brauner Cc: Christian König Cc: Chuck Lever Cc: Daniel Vetter Cc: Daniel Vetter Cc: Darrick J. Wong Cc: Dave Chinner Cc: Greg Kroah-Hartman Cc: Joel Fernandes Cc: Kirill Tkhai Cc: Paul E. McKenney Cc: Roman Gushchin Cc: Sergey Senozhatsky Cc: Steven Price Cc: Theodore Ts'o Cc: Vlastimil Babka Cc: Abhinav Kumar Cc: Alasdair Kergon Cc: Alexander Viro Cc: Alyssa Rosenzweig Cc: Andreas Dilger Cc: Andreas Gruenbacher Cc: Anna Schumaker Cc: Arnd Bergmann Cc: Bob Peterson Cc: Borislav Petkov Cc: Carlos Llamas Cc: Chandan Babu R Cc: Chao Yu Cc: Chris Mason Cc: Coly Li Cc: Dai Ngo Cc: Dave Hansen Cc: David Airlie Cc: David Hildenbrand Cc: David Sterba Cc: Dmitry Baryshkov Cc: Gao Xiang Cc: Huang Rui Cc: Ingo Molnar Cc: Jaegeuk Kim Cc: Jani Nikula Cc: Jan Kara Cc: Jason Wang Cc: Jeff Layton Cc: Jeffle Xu Cc: Joonas Lahtinen Cc: Josef Bacik Cc: Juergen Gross Cc: Kent Overstreet Cc: Marijn Suijten Cc: "Michael S. Tsirkin" Cc: Mike Snitzer Cc: Minchan Kim Cc: Muchun Song Cc: Nadav Amit Cc: Neil Brown Cc: Oleksandr Tyshchenko Cc: Olga Kornievskaia Cc: Richard Weinberger Cc: Rob Clark Cc: Rob Herring Cc: Rodrigo Vivi Cc: Sean Paul Cc: Song Liu Cc: Stefano Stabellini Cc: Thomas Gleixner Cc: Tomeu Vizoso Cc: Tom Talpey Cc: Trond Myklebust Cc: Tvrtko Ursulin Cc: Xuan Zhuo Cc: Yue Hu Signed-off-by: Andrew Morton Stable-dep-of: b902890c62d2 ("mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show()") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mm/damon/reclaim: fix typo in damon_reclaim_timer_fn()

2026-07-24T13:55:08+00:00

Commit 2f54908fae211 ("mm/damon/reclaim: detect and use fresh enabled and kdamond_pid values") introduced a typo in damon_reclaim_timer_fn() where '!=' was used instead of '==' (unlike damon_lru_sort_timer_fn()). This caused damon_reclaim to return early during the delayed work, breaking early boot parameter configuration like 'damon_reclaim.enabled=Y'. Fix this by changing '!=' to '=='. Fixes: 2f54908fae21 ("mm/damon/reclaim: detect and use fresh enabled and kdamond_pid values") Cc: # 6.1.x Reported-by: Yikai Zhao Closes: https://lore.kernel.org/CANMyjpgq5n0Ekt4dgyLRHGb89_Ew0aOMZ3j32V_w0GjHkqH1FQ@mail.gmail.com Reviewed-by: SJ Park Signed-off-by: Liew Rui Yan Signed-off-by: Sasha Levin

mm/damon/ops-common: handle extreme intervals in damon_hot_score()

2026-07-24T13:54:21+00:00

commit 35d4a3cf70a855b50e53189ac2f8463e20a02046 upstream. Fix three issues in damon_hot_score() that comes from wrong handling of extreme (zero or too high) monitoring intervals user setup. When the user sets sampling interval zero, damon_max_nr_accesses(), which is called from damon_hot_score(), causes a divide-by-zero. Needless to say, it is a problem. When the user sets the aggregation interval zero, the function returns zero. It is wrong, since the real maximum nr_acceses in the setup should be one. Worse yet, it can cause another divide-by-zero from its caller, damon_hot_score(), since it uses damon_max_nr_accesses() return value as a denominator. When the user sets the aggregation interval very high, damon_hot_score() could return a value out of [0, DAMOS_MAX_SCORE] range. Since the return value is used as an index to the regions_score_histogram array, which is DAMOS_MAX_SCORE+1 size, it causes out of bounds array access. The issues can be relatively easily reproduced like below. The sysfs write permission is required, though. # ./damo start --damos_action lru_prio --damos_quota_space 100M \ --damos_quota_interval 1s # cd /sys/kernel/mm/damon/admin/kdamonds/0 # echo 0 > contexts/0/monitoring_attrs/intervals/sample_us # echo 0 > contexts/0/monitoring_attrs/intervals/aggr_us # echo commit > state # dmesg [...] [ 131.329762] Oops: divide error: 0000 [#1] SMP NOPTI [...] [ 131.336089] RIP: 0010:damon_hot_score+0x27/0xd0 [...] Fix the divide-by-zero intervals problems by explicitly handling the zero intervals in damon_max_nr_accesses(). Fix the out-of-bound array access by applying [0, DAMOS_MAX_SCORE] bounds before returning from damon_hot_score(). The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260623135834.67189-1-sj@kernel.org Link: https://lore.kernel.org/20260619202459.145010-1-sj@kernel.org [1] Fixes: 198f0f4c58b9 ("mm/damon/vaddr,paddr: support pageout prioritization") Signed-off-by: SeongJae Park Cc: # 5.16.x Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman