From: SJ Park Date: Mon, 3 Aug 2026 13:46:44 +0000 (-0700) Subject: mm/damon/reclaim: skip damon_call() if ctx has not started X-Git-Tag: v7.2-rc7~22^2~5 X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=b9b6bad94c62cbccb9e0ad34635c49fc5f9c52cb;p=thirdparty%2Fkernel%2Flinux.git mm/damon/reclaim: skip damon_call() if ctx has not started Patch series "mm/damon/{reclaim,lru_sort}: fix commit_inputs infinite hang". Writing 'Y' to commit_inputs parameters of DAMON_RECLAIM and DAMON_LRU_SORT before the modules were ever turned on causes infinite hang. Fix those. The issue was discovered [1] by Sashiko. This patch (of 2): DAMON_RECLAIM calls damon_call() for commit_inputs parameter user input if the DAMON context is initialized. The context could be initialized, but not yet successfully started. In the case, damon_call() could indefinitely hang. Read the comment on damon_call() for more detail. Fix the problem by memorizing if the DAMON context has ever successfully started, and skip damon_call() if it has not. This issue can easily be reproduced by writing Y to commit_inputs on a system that DAMON_RECLAIM was not turned on before. Link: https://lore.kernel.org/20260803134646.16640-1-sj@kernel.org Link: https://lore.kernel.org/20260803134646.16640-2-sj@kernel.org Link: https://lore.kernel.org/20260802173021.762-1-sj@kernel.org [1] Fixes: de3c60e1c831 ("mm/damon: add synchronous commit for commit_inputs") Signed-off-by: SJ Park Cc: Liew Rui Yan Cc: # 7.2.x Signed-off-by: Andrew Morton --- diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c index 11b70d0a9a6f..a1a65b1270c8 100644 --- a/mm/damon/reclaim.c +++ b/mm/damon/reclaim.c @@ -276,6 +276,8 @@ static int damon_reclaim_commit_inputs_fn(void *arg) return damon_reclaim_apply_parameters(); } +static bool damon_reclaim_damon_has_started; + static int damon_reclaim_commit_inputs_store(const char *val, const struct kernel_param *kp) { @@ -296,11 +298,8 @@ static int damon_reclaim_commit_inputs_store(const char *val, if (!commit_inputs_request) return 0; - /* - * Skip damon_call() if ctx is not initialized to avoid - * NULL pointer dereference. - */ - if (!ctx) + /* Skip damon_call() if ctx has not successfully started. */ + if (!damon_reclaim_damon_has_started) return -EINVAL; err = damon_call(ctx, &control); @@ -347,6 +346,8 @@ static int damon_reclaim_turn(bool on) err = damon_start(&ctx, 1, true); if (err) return err; + if (!damon_reclaim_damon_has_started) + damon_reclaim_damon_has_started = true; return damon_call(ctx, &call_control); }