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mm/damon/reclaim: skip damon_call() if ctx has not started

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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: de3c60e1c8 ("mm/damon: add synchronous commit for commit_inputs")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: Liew Rui Yan <aethernet65535@gmail.com>
Cc: <stable@vger.kernel.org> # 7.2.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
SJ Park 2026-08-03 06:46:44 -07:00 committed by Andrew Morton
parent 06befa61c4
commit b9b6bad94c
1 changed files with 6 additions and 5 deletions
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11
mm/damon/reclaim.c
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@ -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);
}