linux_dsm_epyc7002/net/sunrpc/auth_gss
Paul Burton c3be6577d8 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
571ed1fd23 ("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 <paul.burton@mips.com>
Fixes: 571ed1fd23 ("SUNRPC: Replace krb5_seq_lock with a lockless scheme")
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Anna Schumaker <anna.schumaker@netapp.com>
Cc: J. Bruce Fields <bfields@fieldses.org>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: linux-nfs@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
2018-11-01 13:55:24 -04:00
..
auth_gss.c SUNRPC: The transmitted message must lie in the RPCSEC window of validity 2018-09-30 15:35:13 -04:00
gss_generic_token.c sunrpc: whitespace fixes 2018-07-31 12:53:40 -04:00
gss_krb5_crypto.c NFS client updates for Linux 4.19 2018-08-23 16:03:58 -07:00
gss_krb5_keys.c sunrpc: whitespace fixes 2018-07-31 12:53:40 -04:00
gss_krb5_mech.c SUNRPC: Use atomic(64)_t for seq_send(64) 2018-11-01 13:55:24 -04:00
gss_krb5_seal.c SUNRPC: Use atomic(64)_t for seq_send(64) 2018-11-01 13:55:24 -04:00
gss_krb5_seqnum.c sunrpc: Use skcipher and ahash/shash 2016-01-27 20:36:01 +08:00
gss_krb5_unseal.c sunrpc: whitespace fixes 2018-07-31 12:53:40 -04:00
gss_krb5_wrap.c SUNRPC: Use atomic(64)_t for seq_send(64) 2018-11-01 13:55:24 -04:00
gss_mech_switch.c SUNRPC: Lockless lookup of RPCSEC_GSS mechanisms 2018-09-30 15:35:17 -04:00
gss_rpc_upcall.c sunrpc: Extract target name into svc_cred 2018-08-22 18:32:07 -04:00
gss_rpc_upcall.h Merge branch 'nfs-for-next' of git://linux-nfs.org/~trondmy/nfs-2.6 into for-3.10 2013-04-29 16:23:34 -04:00
gss_rpc_xdr.c SUNRPC: Add a label for RPC calls that require allocation on receive 2018-09-30 15:35:16 -04:00
gss_rpc_xdr.h sunrpc/auth_gss: fix decoder callback prototypes 2017-07-13 15:57:55 -04:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
svcauth_gss.c sunrpc: whitespace fixes 2018-07-31 12:53:40 -04:00