From c3be6577d82a9f0163eb1e2c37a477414d12a209 Mon Sep 17 00:00:00 2001 From: Paul Burton Date: Thu, 1 Nov 2018 17:51:34 +0000 Subject: SUNRPC: Use atomic(64)_t for seq_send(64) The seq_send & seq_send64 fields in struct krb5_ctx are used as atomically incrementing counters. This is implemented using cmpxchg() & cmpxchg64() to implement what amount to custom versions of atomic_fetch_inc() & atomic64_fetch_inc(). Besides the duplication, using cmpxchg64() has another major drawback in that some 32 bit architectures don't provide it. As such commit 571ed1fd2390 ("SUNRPC: Replace krb5_seq_lock with a lockless scheme") resulted in build failures for some architectures. Change seq_send to be an atomic_t and seq_send64 to be an atomic64_t, then use atomic(64)_* functions to manipulate the values. The atomic64_t type & associated functions are provided even on architectures which lack real 64 bit atomic memory access via CONFIG_GENERIC_ATOMIC64 which uses spinlocks to serialize access. This fixes the build failures for architectures lacking cmpxchg64(). A potential alternative that was raised would be to provide cmpxchg64() on the 32 bit architectures that currently lack it, using spinlocks. However this would provide a version of cmpxchg64() with semantics a little different to the implementations on architectures with real 64 bit atomics - the spinlock-based implementation would only work if all access to the memory used with cmpxchg64() is *always* performed using cmpxchg64(). That is not currently a requirement for users of cmpxchg64(), and making it one seems questionable. As such avoiding cmpxchg64() outside of architecture-specific code seems best, particularly in cases where atomic64_t seems like a better fit anyway. The CONFIG_GENERIC_ATOMIC64 implementation of atomic64_* functions will use spinlocks & so faces the same issue, but with the key difference that the memory backing an atomic64_t ought to always be accessed via the atomic64_* functions anyway making the issue moot. Signed-off-by: Paul Burton Fixes: 571ed1fd2390 ("SUNRPC: Replace krb5_seq_lock with a lockless scheme") Cc: Trond Myklebust Cc: Anna Schumaker Cc: J. Bruce Fields Cc: Jeff Layton Cc: David S. Miller Cc: linux-nfs@vger.kernel.org Cc: netdev@vger.kernel.org Signed-off-by: Trond Myklebust --- include/linux/sunrpc/gss_krb5.h | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) (limited to 'include') diff --git a/include/linux/sunrpc/gss_krb5.h b/include/linux/sunrpc/gss_krb5.h index 69f749afa617..4162de72e95c 100644 --- a/include/linux/sunrpc/gss_krb5.h +++ b/include/linux/sunrpc/gss_krb5.h @@ -107,8 +107,8 @@ struct krb5_ctx { u8 Ksess[GSS_KRB5_MAX_KEYLEN]; /* session key */ u8 cksum[GSS_KRB5_MAX_KEYLEN]; s32 endtime; - u32 seq_send; - u64 seq_send64; + atomic_t seq_send; + atomic64_t seq_send64; struct xdr_netobj mech_used; u8 initiator_sign[GSS_KRB5_MAX_KEYLEN]; u8 acceptor_sign[GSS_KRB5_MAX_KEYLEN]; @@ -118,9 +118,6 @@ struct krb5_ctx { u8 acceptor_integ[GSS_KRB5_MAX_KEYLEN]; }; -extern u32 gss_seq_send_fetch_and_inc(struct krb5_ctx *ctx); -extern u64 gss_seq_send64_fetch_and_inc(struct krb5_ctx *ctx); - /* The length of the Kerberos GSS token header */ #define GSS_KRB5_TOK_HDR_LEN (16) -- cgit v1.2.3-59-g8ed1b