NFS: take a delegation reference in nfs4_get_valid_delegation

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Currently most work on struct nfs_delegation happens directly under RCU
protection.  This is generally fine, despite that long RCU sections are
not good for performance.  But for operations later taking a reference
to the delegation to perform blocking work, refcount_inc is used, which
can be racy against dropping the last reference and thus lead to use
after frees in extremely rare cases.

Fix this by taking a reference in nfs4_get_valid_delegation using
refcount_inc_not_zero so that the callers have a stabilized reference
they can work with and can be moved outside the RCU critical section.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

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Christoph Hellwig 2026-01-07 08:27:08 +01:00 • committed by Anna Schumaker

parent 23e6208755

commit 542b11c072

4 changed files with 56 additions and 46 deletions

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13

fs/nfs/callback_proc.c

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62

fs/nfs/delegation.c

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1

fs/nfs/delegation.h

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26

fs/nfs/nfs4proc.c

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