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Re: [PATCH] xen/grant-table: annotate on-stack work in gnttab_unmap_refs_sync()
- To: Kavitha Daula <kavithadaula@Kavithas-MacBook-Pro.local>, sstabellini@xxxxxxxxxx
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Mon, 9 Nov 2026 09:04:03 +0100
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- Cc: oleksandr_tyshchenko@xxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Kavitha Daula <kavi@xxxxxxxxx>
- Delivery-date: Mon, 09 Nov 2026 08:04:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 05.11.26 01:01, Kavitha Daula wrote:
From: Kavitha Daula <kavi@xxxxxxxxx>
Both callers of gnttab_unmap_refs_sync(), free_persistent_gnts() and
xen_blkbk_unmap_purged_grants() in blkback, keep their struct
gntab_unmap_queue_data on the stack. gnttab_unmap_refs_async() sets up
the delayed work inside it with INIT_DELAYED_WORK(), so with
CONFIG_DEBUG_OBJECTS_WORK and CONFIG_DEBUG_OBJECTS_TIMERS every
persistent grant teardown warns twice, once for the work and once for
its timer:
[ 104.366085] ODEBUG: object ffffc9004020fad8 is on stack ffffc9004020c000,
but NOT annotated.
[ 104.371551] WARNING: CPU: 1 PID: 48 at lib/debugobjects.c:672
lookup_object_or_alloc.part.0+0x12b/0x1f0
Call Trace:
<TASK>
__debug_object_init+0xfe/0x1a0
debug_object_init+0x38/0x50
__init_work+0x28/0x30
gnttab_unmap_refs_async+0x18/0xa0
gnttab_unmap_refs_sync+0x61/0x90
free_persistent_gnts+0x179/0x280
xen_blkbk_free_caches+0x16/0x30
xen_blkif_disconnect+0xfa/0x2d0
frontend_changed+0x90/0x680
xenbus_otherend_changed+0x80/0xb0
frontend_changed+0x14/0x20
xenwatch_thread+0x96/0x1a0
kthread+0x11d/0x250
ret_from_fork+0x29f/0x2d0
ret_from_fork_asm+0x1a/0x30
</TASK>
gnttab_unmap_refs_sync() waits for the unmap to complete before it
returns, so the work never outlives the caller's frame. Initialise it
with INIT_DELAYED_WORK_ONSTACK() when the item is on the stack and
destroy it before returning. The function is exported, so an item that
is not on the stack keeps INIT_DELAYED_WORK().
Fixes: b44166cd46e2 ("xen/grant: introduce func gnttab_unmap_refs_sync()")
Signed-off-by: Kavitha Daula <kavi@xxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Juergen
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