Re: [PATCH] nvme-tcp: fix usage of page_frag_cache

[Daniel Wagner]

On Thu, Jul 16, 2026 at 04:42:19PM +0200, Daniel Wagner wrote:
> From: Dmitry Bogdanov <d.bogdanov@xxxxxxxxx>
> 
> nvme uses page_frag_cache to preallocate PDU for each preallocated request
> of block device. Block devices are created in parallel threads,
> consequently page_frag_cache is used in not thread-safe manner.
> That leads to incorrect refcounting of backstore pages and premature free.
> 
> That can be catched by !sendpage_ok inside network stack:
> 
> WARNING: CPU: 7 PID: 467 at ../net/core/skbuff.c:6931 skb_splice_from_iter+0xfa/0x310.
> 	tcp_sendmsg_locked+0x782/0xce0
> 	tcp_sendmsg+0x27/0x40
> 	sock_sendmsg+0x8b/0xa0
> 	nvme_tcp_try_send_cmd_pdu+0x149/0x2a0
> Then random panic may occur.
> 
> Fix that by serializing the usage of page_frag_cache.
> 
> Fixes: 4e893ca81170 ("nvme_core: scan namespaces asynchronously")
> Signed-off-by: Dmitry Bogdanov <d.bogdanov@xxxxxxxxx>
> Signed-off-by: Daniel Wagner <wagi@xxxxxxxxxx>
> ---
> If the target exposes many namespaces (>1000) and the host has many CPUs (>80),
> it is trivial to trigger the allocation race condition in nvme_tcp_init_request
> which results in the logs below:

Any chance to move forward with this on?