Re: [PATCH] net: page_pool: Remove zone/policy GFP flags when allocating XArray entries

Rong Zhang <[email protected]> writes:

> Net drivers request GFP flags according to both the current context and
> the device constraints, but the XArray entry itself is by no mean used
> by the device. Passing though device constraints to XArray allocation is
> a bug and will be warned and fixed up by slab, e.g.:
>
>     Unexpected gfp: 0x4 (GFP_DMA32). Fixing up to gfp: 0x82820 (GFP_ATOMIC|__GFP_NOWARN|__GFP_NOMEMALLOC). Fix your code!
>     CPU: 2 UID: 0 PID: 1071629 Comm: kworker/u80:1 Not tainted 7.2.0-rc7+ #1 PREEMPT(lazy)
>     Hardware name: LENOVO 21Q4/LNVNB161216, BIOS PXCN27WW 10/20/2025
>     Workqueue: mt76 mt792x_pm_wake_work [mt792x_lib]
>     Call Trace:
>      <TASK>
>      dump_stack_lvl+0x6e/0x90
>      kmalloc_fix_flags+0x4d/0x6a
>      refill_objects+0x10a/0x330
>      __pcs_replace_empty_main+0x292/0x5c0
>      kmem_cache_alloc_lru_noprof+0x4c2/0x680
>      ? __xas_nomem+0x3a/0x120
>      __xas_nomem+0x3a/0x120
>      __xa_alloc+0xd4/0x190
>      page_pool_dma_map+0xef/0x400
>      __page_pool_alloc_netmems_slow+0xed/0x480
>      ? lock_release+0x280/0x490
>      page_pool_alloc_frag_netmem+0xe0/0x3a0
>      page_pool_alloc_frag+0xe/0x20
>      mt76_dma_rx_fill_buf+0x1f6/0x580 [mt76]
>      mt76_dma_rx_reset+0x1cf/0x230 [mt76]
>      mt792x_wpdma_reset+0x183/0x1b0 [mt792x_lib]
>      mt792x_wpdma_reinit_cond+0x5e/0xa0 [mt792x_lib]
>      mt792xe_mcu_drv_pmctrl+0x28/0x60 [mt792x_lib]
>      mt792x_mcu_drv_pmctrl+0x3e/0x90 [mt792x_lib]
>      mt792x_pm_wake_work+0x2d/0x1d0 [mt792x_lib]
>      ? process_one_work+0x20e/0x600
>      process_one_work+0x230/0x600
>      ? process_one_work+0x256/0x600
>      worker_thread+0x1ec/0x3c0
>      ? rescuer_thread+0x610/0x610
>      kthread+0xf2/0x130
>      ? kthread_affine_node+0x140/0x140
>      ret_from_fork+0x2a5/0x380
>      ? kthread_affine_node+0x140/0x140
>      ret_from_fork_asm+0x11/0x20
>      </TASK>
>
> Currently mt76 and stmmac may allocate page pool pages with GFP_DMA32.
>
> Fix it by removing zone/policy GFP flags when allocating XArray entries.
> This is inspired by commit 96d578088085 ("iommu/dma: Use the gfp
> parameter in __iommu_dma_alloc_noncontiguous()").
>
> Fixes: ee62ce7a1d90 ("page_pool: Track DMA-mapped pages and unmap them when destroying the pool")
> Signed-off-by: Rong Zhang <[email protected]>

Reviewed-by: Toke Høiland-Jørgensen <[email protected]>