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* FAILED: patch "[PATCH] mm/damon/core: avoid use of half-online-committed context" failed to apply to 6.19-stable tree
@ 2026-03-29  7:25 gregkh
  2026-03-29 16:21 ` [PATCH 6.19.y] mm/damon/core: avoid use of half-online-committed context SeongJae Park
  0 siblings, 1 reply; 2+ messages in thread
From: gregkh @ 2026-03-29  7:25 UTC (permalink / raw)
  To: sj, akpm, stable; +Cc: stable


The patch below does not apply to the 6.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.19.y
git checkout FETCH_HEAD
git cherry-pick -x 26f775a054c3cda86ad465a64141894a90a9e145
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026032924-italicize-animate-f383@gregkh' --subject-prefix 'PATCH 6.19.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 26f775a054c3cda86ad465a64141894a90a9e145 Mon Sep 17 00:00:00 2001
From: SeongJae Park <sj@kernel.org>
Date: Thu, 19 Mar 2026 07:52:17 -0700
Subject: [PATCH] mm/damon/core: avoid use of half-online-committed context

One major usage of damon_call() is online DAMON parameters update.  It is
done by calling damon_commit_ctx() inside the damon_call() callback
function.  damon_commit_ctx() can fail for two reasons: 1) invalid
parameters and 2) internal memory allocation failures.  In case of
failures, the damon_ctx that attempted to be updated (commit destination)
can be partially updated (or, corrupted from a perspective), and therefore
shouldn't be used anymore.  The function only ensures the damon_ctx object
can safely deallocated using damon_destroy_ctx().

The API callers are, however, calling damon_commit_ctx() only after
asserting the parameters are valid, to avoid damon_commit_ctx() fails due
to invalid input parameters.  But it can still theoretically fail if the
internal memory allocation fails.  In the case, DAMON may run with the
partially updated damon_ctx.  This can result in unexpected behaviors
including even NULL pointer dereference in case of damos_commit_dests()
failure [1].  Such allocation failure is arguably too small to fail, so
the real world impact would be rare.  But, given the bad consequence, this
needs to be fixed.

Avoid such partially-committed (maybe-corrupted) damon_ctx use by saving
the damon_commit_ctx() failure on the damon_ctx object.  For this,
introduce damon_ctx->maybe_corrupted field.  damon_commit_ctx() sets it
when it is failed.  kdamond_call() checks if the field is set after each
damon_call_control->fn() is executed.  If it is set, ignore remaining
callback requests and return.  All kdamond_call() callers including
kdamond_fn() also check the maybe_corrupted field right after
kdamond_call() invocations.  If the field is set, break the kdamond_fn()
main loop so that DAMON sill doesn't use the context that might be
corrupted.

[sj@kernel.org: let kdamond_call() with cancel regardless of maybe_corrupted]
  Link: https://lkml.kernel.org/r/20260320031553.2479-1-sj@kernel.org
  Link: https://sashiko.dev/#/patchset/20260319145218.86197-1-sj%40kernel.org
Link: https://lkml.kernel.org/r/20260319145218.86197-1-sj@kernel.org
Link: https://lore.kernel.org/20260319043309.97966-1-sj@kernel.org [1]
Fixes: 3301f1861d34 ("mm/damon/sysfs: handle commit command using damon_call()")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[6.15+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/damon.h b/include/linux/damon.h
index a4fea23da857..be3d198043ff 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -810,6 +810,12 @@ struct damon_ctx {
 	struct damos_walk_control *walk_control;
 	struct mutex walk_control_lock;
 
+	/*
+	 * indicate if this may be corrupted.  Currentonly this is set only for
+	 * damon_commit_ctx() failure.
+	 */
+	bool maybe_corrupted;
+
 	/* Working thread of the given DAMON context */
 	struct task_struct *kdamond;
 	/* Protects @kdamond field access */
diff --git a/mm/damon/core.c b/mm/damon/core.c
index c1d1091d307e..3e1890d64d06 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1252,6 +1252,7 @@ int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src)
 {
 	int err;
 
+	dst->maybe_corrupted = true;
 	if (!is_power_of_2(src->min_region_sz))
 		return -EINVAL;
 
@@ -1277,6 +1278,7 @@ int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src)
 	dst->addr_unit = src->addr_unit;
 	dst->min_region_sz = src->min_region_sz;
 
+	dst->maybe_corrupted = false;
 	return 0;
 }
 
@@ -2678,6 +2680,8 @@ static void kdamond_call(struct damon_ctx *ctx, bool cancel)
 			complete(&control->completion);
 		else if (control->canceled && control->dealloc_on_cancel)
 			kfree(control);
+		if (!cancel && ctx->maybe_corrupted)
+			break;
 	}
 
 	mutex_lock(&ctx->call_controls_lock);
@@ -2707,6 +2711,8 @@ static int kdamond_wait_activation(struct damon_ctx *ctx)
 		kdamond_usleep(min_wait_time);
 
 		kdamond_call(ctx, false);
+		if (ctx->maybe_corrupted)
+			return -EINVAL;
 		damos_walk_cancel(ctx);
 	}
 	return -EBUSY;
@@ -2790,6 +2796,8 @@ static int kdamond_fn(void *data)
 		 * kdamond_merge_regions() if possible, to reduce overhead
 		 */
 		kdamond_call(ctx, false);
+		if (ctx->maybe_corrupted)
+			break;
 		if (!list_empty(&ctx->schemes))
 			kdamond_apply_schemes(ctx);
 		else


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2026-03-29  7:25 FAILED: patch "[PATCH] mm/damon/core: avoid use of half-online-committed context" failed to apply to 6.19-stable tree gregkh
2026-03-29 16:21 ` [PATCH 6.19.y] mm/damon/core: avoid use of half-online-committed context SeongJae Park

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