Re: [PATCH] netfs: Fix missing alloc tagging of direct mempool allocations

[Suren Baghdasaryan]

On Mon, Sep 21, 2026 at 7:37 PM Hao Ge <hao.ge@xxxxxxxxx> wrote:
>
> Commit 1d78d56c43ef ("netfs: Fix folio_queue ENOMEM in writeback by
> adding a mempool") added a mempool for the folio_queues and made the
> request, subrequest and folio_queue allocations distinguish between
> writeback and everything else.  Writeback is part of memory reclaim
> and must not fail due to ENOMEM, so it allocates under GFP_NOFS
> through mempool_alloc(), which may dip into the pool's reserve and,
> if that runs empty, wait for elements to be returned.  The
> GFP_KERNEL paths, which can return -ENOMEM to their callers, invoke
> the pool's ->alloc() callback directly instead.
>
> The direct call, however, skips the alloc_hooks() wrapper that the
> mempool_alloc() macro provides.  The pool callbacks, mempool_alloc_slab()
> and mempool_kmalloc(), call kmem_cache_alloc_noprof() and kmalloc_noprof()
> and rely on current->alloc_tag having been set by the caller.  With
> CONFIG_MEM_ALLOC_PROFILING_DEBUG=y this leads to
>
>     current->alloc_tag not set
>     WARNING: ./include/linux/alloc_tag.h:161 at __alloc_tagging_slab_alloc_hook
>     alloc_tag was not set
>     WARNING: ./include/linux/alloc_tag.h:166 at __alloc_tagging_slab_free_hook
>
> at allocation and free time respectively, as reported when reading
> files on a CIFS mount.  The allocations are also missing from
> /proc/allocinfo.
>
> Wrap the direct ->alloc() invocations in alloc_hooks() with the new
> netfs_mempool_alloc_noreserve() helper.  The GFP_KERNEL paths keep their
> failable allocation semantics, they just get tagged now.
>
> Fixes: 1d78d56c43ef ("netfs: Fix folio_queue ENOMEM in writeback by adding a mempool")
> Reported-by: Erhard Furtner <erhard_f@xxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/0b004319-9ef7-437c-a4dd-174d6a9a83db@xxxxxxxxxxx/
> Tested-by: Erhard Furtner <erhard_f@xxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Hao Ge <hao.ge@xxxxxxxxx>
> ---
>  fs/netfs/internal.h       | 3 +++
>  fs/netfs/objects.c        | 4 ++--
>  fs/netfs/rolling_buffer.c | 2 +-
>  3 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
> index c79c8e69d60c..08ba7f0ebff0 100644
> --- a/fs/netfs/internal.h
> +++ b/fs/netfs/internal.h
> @@ -45,6 +45,9 @@ extern mempool_t netfs_request_pool;
>  extern mempool_t netfs_subrequest_pool;
>  extern mempool_t netfs_folioq_pool;
>
> +#define netfs_mempool_alloc_noreserve(_pool, _gfp)                             \
> +       alloc_hooks((_pool)->alloc(_gfp, (_pool)->pool_data))

I think this macro should reside in include/linux/mempool.h and not be
netfs-specific. Something like:

#define mempool_alloc_noreserve(_pool, _gfp)                             \
       alloc_hooks((_pool)->alloc(_gfp, (_pool)->pool_data))

> +
>  #ifdef CONFIG_PROC_FS
>  static inline void netfs_proc_add_rreq(struct netfs_io_request *rreq)
>  {
> diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
> index 7f6a3e912602..0b509c93d4af 100644
> --- a/fs/netfs/objects.c
> +++ b/fs/netfs/objects.c
> @@ -34,7 +34,7 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
>
>                 rreq = mempool_alloc(mempool, gfp);
>         } else {
> -               rreq = mempool->alloc(gfp, mempool->pool_data);
> +               rreq = netfs_mempool_alloc_noreserve(mempool, gfp);
>                 if (!rreq)
>                         return ERR_PTR(-ENOMEM);
>         }
> @@ -214,7 +214,7 @@ struct netfs_io_subrequest *netfs_alloc_subrequest(struct netfs_io_request *rreq
>         struct kmem_cache *cache = mempool->pool_data;
>
>         if (rreq->gfp == GFP_KERNEL)
> -               subreq = mempool->alloc(rreq->gfp, mempool->pool_data);
> +               subreq = netfs_mempool_alloc_noreserve(mempool, rreq->gfp);
>         else
>                 subreq = mempool_alloc(mempool, rreq->gfp);
>         if (!subreq)
> diff --git a/fs/netfs/rolling_buffer.c b/fs/netfs/rolling_buffer.c
> index 424e77a9a109..54867ceaa205 100644
> --- a/fs/netfs/rolling_buffer.c
> +++ b/fs/netfs/rolling_buffer.c
> @@ -29,7 +29,7 @@ struct folio_queue *netfs_folioq_alloc(unsigned int rreq_id, gfp_t gfp,
>         struct folio_queue *fq;
>
>         if (gfp == GFP_KERNEL)
> -               fq = netfs_folioq_pool.alloc(gfp, netfs_folioq_pool.pool_data);
> +               fq = netfs_mempool_alloc_noreserve(&netfs_folioq_pool, gfp);
>         else
>                 fq = mempool_alloc(&netfs_folioq_pool, gfp);
>         if (fq) {
> --
> 2.25.1
>
>