[PATCH 7.1.y] samples/damon/mtier: fail early if address range parameters are invalid

[PATCH 7.1.y] samples/damon/mtier: fail early if address range parameters are invalid

[SJ Park]

From: Zenghui Yu <yuzenghui@huawei.com>

The comment on top of `struct damon_region` clearly says that

    For any use case, @ar should be non-zero positive size.

which is now verified in damon_verify_new_region() if the kernel is built
with DAMON_DEBUG_SANITY.

The WARN_ONCE() can be triggered if the mtier sample module is enabled
before node{0,1}_{start,end}_addr have been properly initialized, which is
obviously not good.

 ------------[ cut here ]------------
 start 0 >= end 0
 WARNING: mm/damon/core.c:217 at damon_new_region+0xf4/0x118, CPU#59: bash/341468
 Call trace:
  damon_new_region+0xf4/0x118 (P)
  damon_set_regions+0xfc/0x3c0
  damon_sample_mtier_build_ctx+0xe8/0x3a8
  damon_sample_mtier_start+0x1c/0x90
  damon_sample_mtier_enable_store+0x98/0xb0
  param_attr_store+0xb4/0x128
  module_attr_store+0x2c/0x50
  sysfs_kf_write+0x58/0x90
  kernfs_fop_write_iter+0x16c/0x238
  vfs_write+0x2c0/0x370
  ksys_write+0x74/0x118
  __arm64_sys_write+0x24/0x38
  invoke_syscall+0xa8/0x118
  el0_svc_common.constprop.0+0x48/0xf0
  do_el0_svc+0x24/0x38
  el0_svc+0x54/0x370
  el0t_64_sync_handler+0xa0/0xe8
  el0t_64_sync+0x1ac/0x1b0
 ---[ end trace 0000000000000000 ]---

Note that the same issue can happen if detect_node_addresses is true, and
node 0 or 1 is memoryless.  Fix it together by checking the validity of
parameters right before damon_new_region() and fail early if they're
invalid.

Link: https://lore.kernel.org/20260629144432.133962-1-sj@kernel.org
Fixes: 82a08bde3cf7 ("samples/damon: implement a DAMON module for memory tiering")
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: SJ Park <sj@kernel.org>
Reviewed-by: SJ Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.16.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 7746d72c64054976887928d64d2caf25c5a6dcc0)
Signed-off-by: SJ Park <sj@kernel.org>
---
 samples/damon/mtier.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/samples/damon/mtier.c b/samples/damon/mtier.c
index 775838a23d935..7f84367ad3e58 100644
--- a/samples/damon/mtier.c
+++ b/samples/damon/mtier.c
@@ -120,6 +120,9 @@ static struct damon_ctx *damon_sample_mtier_build_ctx(bool promote)
 		addr.end = promote ? node1_end_addr : node0_end_addr;
 	}
 
+	if (addr.start >= addr.end)
+		goto free_out;
+
 	region = damon_new_region(addr.start, addr.end);
 	if (!region)
 		goto free_out;
-- 
2.47.3

Re: [PATCH 7.1.y] samples/damon/mtier: fail early if address range parameters are invalid

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Resource leaks (memory, kthreads, struct pid) on failure paths in DAMON sample modules.
--

--- Patch [1]: [PATCH 7.1.y] samples/damon/mtier: fail early if address range parameters are invalid ---
commit 999f01f2d7c2530ae577d445b6761ac7a2a10e77
Author: Zenghui Yu <yuzenghui@huawei.com>

samples/damon/mtier: fail early if address range parameters are invalid

This commit prevents a WARN_ONCE() trigger in the damon mtier sample module
by validating that node{0,1}_{start,end}_addr specify a valid region
before passing them to damon_new_region().

Link: https://lore.kernel.org/20260629144432.133962-1-sj@kernel.org

> diff --git a/samples/damon/mtier.c b/samples/damon/mtier.c
> index 775838a23d935..7f84367ad3e58 100644
> --- a/samples/damon/mtier.c
> +++ b/samples/damon/mtier.c
> @@ -120,6 +120,9 @@ static struct damon_ctx *damon_sample_mtier_build_ctx(bool promote)
>  		addr.end = promote ? node1_end_addr : node0_end_addr;
>  	}
>  
> +	if (addr.start >= addr.end)
> +		goto free_out;
> +
>  	region = damon_new_region(addr.start, addr.end);
>  	if (!region)
>  		goto free_out;

[Severity: High]
This is a pre-existing issue, but does damon_sample_mtier_start() leak memory 
and running kthreads on failure?

Looking at samples/damon/mtier.c:damon_sample_mtier_start():

	return damon_start(ctxs, 2, true);

If damon_start() succeeds for the first context but fails for the second, the
error is returned directly. This leaves the first context running
indefinitely, leaking both the damon_ctx objects and the started kthreads.
This would hold the damon core's exclusive flag, preventing future exclusive
monitoring on the system until reboot.

A similar issue appears in samples/damon/prcl.c:damon_sample_prcl_start():

	err = damon_start(&ctx, 1, true);
	if (err)
		return err;

	repeat_call_control.data = ctx;
	return damon_call(ctx, &repeat_call_control);

And in samples/damon/wsse.c:damon_sample_wsse_start():

	err = damon_start(&ctx, 1, true);
	if (err)
		return err;

	repeat_call_control.data = ctx;
	return damon_call(ctx, &repeat_call_control);

If damon_call() fails, the functions return the error immediately without
stopping the started threads or destroying the contexts. This also bypasses 
damon_destroy_ctx(), leading to a struct pid reference leak.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260721053953.181336-1-sj@kernel.org?part=1