[PATCH] virtio_console: allocate the port_buffer with the caller's gfp

[PATCH] virtio_console: allocate the port_buffer with the caller's gfp

[Breno Leitao]

put_chars() runs from the hvc console write path with preemption
disabled, so it asks alloc_buf() for GFP_ATOMIC. Only the data buffer
gets it: the struct port_buffer itself keeps the GFP_KERNEL default, so
the allocation can enter direct reclaim and sleep. A write to /dev/kmsg
on a CONFIG_DEBUG_ATOMIC_SLEEP kernel splats:

  BUG: sleeping function called from invalid context at ./include/linux/sched/mm.h:320
  in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 1, name: virtme-ng-init
  preempt_count: 1, expected: 0
  Preemption disabled at:
  [<ffffffff813fd90d>] vprintk_emit+0x17d/0x510
  Call Trace:
   <TASK>
   dump_stack_lvl+0x69/0xa0
   __might_resched+0x37a/0x4d0
   __kmalloc_cache_noprof+0x94/0x5f0
   put_chars+0x209/0x3e0
   hvc_console_print+0x234/0x640
   console_flush_all+0x4fc/0x950
   console_unlock+0xbf/0x1b0
   vprintk_emit+0x312/0x510
   devkmsg_emit+0xba/0x110
   devkmsg_write+0x21b/0x2e0
   vfs_write+0x4dc/0x9d0
   ksys_write+0x108/0x1e0
   do_syscall_64+0xfa/0x460
   </TASK>

Pass gfp on to that allocation too.

Fixes: fc220d6be3c7 ("virtio_console: refactor __send_to_port() buffer ownership")
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/char/virtio_console.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 62eecfa61646d..7f6cbe851d1e1 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -426,7 +426,7 @@ static struct port_buffer *alloc_buf(struct virtio_device *vdev, size_t buf_size
 	 * Allocate buffer and the sg list. The sg list array is allocated
 	 * directly after the port_buffer struct.
 	 */
-	buf = kmalloc_flex(*buf, sg, pages);
+	buf = kmalloc_flex(*buf, sg, pages, gfp);
 	if (!buf)
 		goto fail;
 

---
base-commit: 6b8c8af514d739d0335f5579b585e02babe8a727
change-id: 20260810-serial-d9b259ec9100

Best regards,
--  
Breno Leitao <leitao@debian.org>

Re: [PATCH] virtio_console: allocate the port_buffer with the caller's gfp

[Breno Leitao]

On Mon, Aug 10, 2026 at 09:40:00AM -0700, Breno Leitao wrote:
> put_chars() runs from the hvc console write path with preemption
> disabled, so it asks alloc_buf() for GFP_ATOMIC. Only the data buffer
> gets it: the struct port_buffer itself keeps the GFP_KERNEL default, so
> the allocation can enter direct reclaim and sleep. A write to /dev/kmsg
> on a CONFIG_DEBUG_ATOMIC_SLEEP kernel splats:
> 
>   BUG: sleeping function called from invalid context at ./include/linux/sched/mm.h:320
>   in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 1, name: virtme-ng-init
>   preempt_count: 1, expected: 0
>   Preemption disabled at:
>   [<ffffffff813fd90d>] vprintk_emit+0x17d/0x510
>   Call Trace:
>    <TASK>
>    dump_stack_lvl+0x69/0xa0
>    __might_resched+0x37a/0x4d0
>    __kmalloc_cache_noprof+0x94/0x5f0
>    put_chars+0x209/0x3e0
>    hvc_console_print+0x234/0x640
>    console_flush_all+0x4fc/0x950
>    console_unlock+0xbf/0x1b0
>    vprintk_emit+0x312/0x510
>    devkmsg_emit+0xba/0x110
>    devkmsg_write+0x21b/0x2e0
>    vfs_write+0x4dc/0x9d0
>    ksys_write+0x108/0x1e0
>    do_syscall_64+0xfa/0x460
>    </TASK>
> 
> Pass gfp on to that allocation too.
> 
> Fixes: fc220d6be3c7 ("virtio_console: refactor __send_to_port() buffer ownership")
> Signed-off-by: Breno Leitao <leitao@debian.org>

Ping?