From b4868b44c5628995fdd8ef2e24dda73cef963a75 Mon Sep 17 00:00:00 2001 From: Benjamin Coddington Date: Fri, 25 Sep 2020 15:48:39 -0400 Subject: NFSv4: Wait for stateid updates after CLOSE/OPEN_DOWNGRADE Since commit 0e0cb35b417f ("NFSv4: Handle NFS4ERR_OLD_STATEID in CLOSE/OPEN_DOWNGRADE") the following livelock may occur if a CLOSE races with the update of the nfs_state: Process 1 Process 2 Server ========= ========= ======== OPEN file OPEN file Reply OPEN (1) Reply OPEN (2) Update state (1) CLOSE file (1) Reply OLD_STATEID (1) CLOSE file (2) Reply CLOSE (-1) Update state (2) wait for state change OPEN file wake CLOSE file OPEN file wake CLOSE file ... ... We can avoid this situation by not issuing an immediate retry with a bumped seqid when CLOSE/OPEN_DOWNGRADE receives NFS4ERR_OLD_STATEID. Instead, take the same approach used by OPEN and wait at least 5 seconds for outstanding stateid updates to complete if we can detect that we're out of sequence. Note that after this change it is still possible (though unlikely) that CLOSE waits a full 5 seconds, bumps the seqid, and retries -- and that attempt races with another OPEN at the same time. In order to avoid this race (which would result in the livelock), update nfs_need_update_open_stateid() to handle the case where: - the state is NFS_OPEN_STATE, and - the stateid doesn't match the current open stateid Finally, nfs_need_update_open_stateid() is modified to be idempotent and renamed to better suit the purpose of signaling that the stateid passed is the next stateid in sequence. Fixes: 0e0cb35b417f ("NFSv4: Handle NFS4ERR_OLD_STATEID in CLOSE/OPEN_DOWNGRADE") Cc: stable@vger.kernel.org # v5.4+ Signed-off-by: Benjamin Coddington Signed-off-by: Anna Schumaker --- fs/nfs/nfs4_fs.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'fs/nfs/nfs4_fs.h') diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h index 0c9505dc852c..065cb04222a1 100644 --- a/fs/nfs/nfs4_fs.h +++ b/fs/nfs/nfs4_fs.h @@ -599,6 +599,14 @@ static inline bool nfs4_stateid_is_newer(const nfs4_stateid *s1, const nfs4_stat return (s32)(be32_to_cpu(s1->seqid) - be32_to_cpu(s2->seqid)) > 0; } +static inline bool nfs4_stateid_is_next(const nfs4_stateid *s1, const nfs4_stateid *s2) +{ + u32 seq1 = be32_to_cpu(s1->seqid); + u32 seq2 = be32_to_cpu(s2->seqid); + + return seq2 == seq1 + 1U || (seq2 == 1U && seq1 == 0xffffffffU); +} + static inline bool nfs4_stateid_match_or_older(const nfs4_stateid *dst, const nfs4_stateid *src) { return nfs4_stateid_match_other(dst, src) && -- cgit v1.2.3-58-ga151