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netfs: Fix missing alloc tagging of direct mempool allocations

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Commit 1d78d56c43 ("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 a new
mempool_alloc_noreserve() helper in include/linux/mempool.h, next to
the other alloc_hooks()-wrapped macros such as mempool_alloc().  The
GFP_KERNEL paths keep their failable allocation semantics, they just
get tagged now.

Fixes: 1d78d56c43 ("netfs: Fix folio_queue ENOMEM in writeback by adding a mempool")
Reported-by: Erhard Furtner <erhard_f@mailbox.org>
Closes: https://lore.kernel.org/all/0b004319-9ef7-437c-a4dd-174d6a9a83db@mailbox.org/
Tested-by: Erhard Furtner <erhard_f@mailbox.org>
Suggested-by: Suren Baghdasaryan <surenb@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Hao Ge <hao.ge@linux.dev>
Link: https://patch.msgid.link/20260923063759.34667-1-hao.ge@linux.dev
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Hao Ge 2026-09-23 14:37:59 +08:00 • committed by Christian Brauner
commit b78b728e21
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3 changed files with 10 additions and 3 deletions
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