From f3734cc4073f68ac3566293acc6d62971c47ad5a Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 26 Oct 2023 16:50:18 +0200 Subject: [PATCH] NFSD: use read_seqbegin() rather than read_seqbegin_or_lock() The usage of read_seqbegin_or_lock() in nfsd_copy_write_verifier() is wrong. "seq" is always even and thus "or_lock" has no effect, this code can never take ->writeverf_lock for writing. I guess this is fine, nfsd_copy_write_verifier() just copies 8 bytes and nfsd_reset_write_verifier() is supposed to be very rare operation so we do not need the adaptive locking in this case. Yet the code looks wrong and sub-optimal, it can use read_seqbegin() without changing the behaviour. [ cel: Note also that it eliminates this Sparse warning: fs/nfsd/nfssvc.c:360:6: warning: context imbalance in 'nfsd_copy_write_verifier' - different lock contexts for basic block ] Signed-off-by: Oleg Nesterov Reviewed-by: Jeff Layton Reviewed-by: NeilBrown Signed-off-by: Chuck Lever --- fs/nfsd/nfssvc.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c index 7a2bc8e82a63..ee835bf9ee42 100644 --- a/fs/nfsd/nfssvc.c +++ b/fs/nfsd/nfssvc.c @@ -359,13 +359,12 @@ static bool nfsd_needs_lockd(struct nfsd_net *nn) */ void nfsd_copy_write_verifier(__be32 verf[2], struct nfsd_net *nn) { - int seq = 0; + unsigned int seq; do { - read_seqbegin_or_lock(&nn->writeverf_lock, &seq); + seq = read_seqbegin(&nn->writeverf_lock); memcpy(verf, nn->writeverf, sizeof(nn->writeverf)); - } while (need_seqretry(&nn->writeverf_lock, seq)); - done_seqretry(&nn->writeverf_lock, seq); + } while (read_seqretry(&nn->writeverf_lock, seq)); } static void nfsd_reset_write_verifier_locked(struct nfsd_net *nn)