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

[Breno Leitao <leitao@debian.org>]

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>

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