On Wed, 2018-10-31 at 18:18 -0700, Guenter Roeck wrote: > On 10/31/18 4:32 PM, Paul Burton wrote: > > (Copying SunRPC & net maintainers.) > > > > Hi Guenter, > > > > On Wed, Oct 31, 2018 at 03:02:53PM -0700, Guenter Roeck wrote: > > > The alternatives I can see are > > > - Do not use cmpxchg64() outside architecture code (ie drop its > > > use from > > > the offending driver, and keep doing the same whenever the > > > problem comes > > > up again). > > > or > > > - Introduce something like ARCH_HAS_CMPXCHG64 and use it to > > > determine > > > if cmpxchg64 is supported or not. > > > > > > Any preference ? > > > > My preference would be option 1 - avoiding cmpxchg64() where > > possible in > > generic code. I wouldn't be opposed to the Kconfig option if there > > are > > cases where cmpxchg64() can really help performance though. > > > > The last time I'm aware of this coming up the affected driver was > > modified to avoid cmpxchg64() [1]. > > > > In this particular case I have no idea why > > net/sunrpc/auth_gss/gss_krb5_seal.c is using cmpxchg64() at all. > > It's > > essentially reinventing atomic64_fetch_inc() which is already > > provided > > everywhere via CONFIG_GENERIC_ATOMIC64 & the spinlock approach. At > > least > > for atomic64_* functions the assumption that all access will be > > performed using those same functions seems somewhat reasonable. > > > > So how does the below look? Trond? > > > > For my part I agree that this would be a much better solution. The > argument > that it is not always absolutely guaranteed that atomics don't wrap > doesn't > really hold for me because it looks like they all do. On top of that, > there > is an explicit atomic_dec_if_positive() and > atomic_fetch_add_unless(), > which to me strongly suggests that they _are_ supposed to wrap. > Given the cost of adding a comparison to each atomic operation to > prevent it from wrapping, anything else would not really make sense > to me.
That's a hypothesis, not a proven fact. There are architectures out there that do not wrap signed integers, hence my question. > So ... please consider my patch abandoned. Thanks for looking into > this! > > Guenter > > > Thanks, > > Paul > > > > [1] https://patchwork.ozlabs.org/cover/891284/ > > > > --- > > diff --git a/include/linux/sunrpc/gss_krb5.h > > b/include/linux/sunrpc/gss_krb5.h > > index 131424cefc6a..02c0412e368c 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) > > > > diff --git a/net/sunrpc/auth_gss/gss_krb5_mech.c > > b/net/sunrpc/auth_gss/gss_krb5_mech.c > > index 7f0424dfa8f6..eab71fc7af3e 100644 > > --- a/net/sunrpc/auth_gss/gss_krb5_mech.c > > +++ b/net/sunrpc/auth_gss/gss_krb5_mech.c > > @@ -274,6 +274,7 @@ get_key(const void *p, const void *end, > > static int > > gss_import_v1_context(const void *p, const void *end, struct > > krb5_ctx *ctx) > > { > > + u32 seq_send; > > int tmp; > > > > p = simple_get_bytes(p, end, &ctx->initiate, sizeof(ctx- > > >initiate)); > > @@ -315,9 +316,10 @@ gss_import_v1_context(const void *p, const > > void *end, struct krb5_ctx *ctx) > > p = simple_get_bytes(p, end, &ctx->endtime, sizeof(ctx- > > >endtime)); > > if (IS_ERR(p)) > > goto out_err; > > - p = simple_get_bytes(p, end, &ctx->seq_send, sizeof(ctx- > > >seq_send)); > > + p = simple_get_bytes(p, end, &seq_send, sizeof(seq_send)); > > if (IS_ERR(p)) > > goto out_err; > > + atomic_set(&ctx->seq_send, seq_send); > > p = simple_get_netobj(p, end, &ctx->mech_used); > > if (IS_ERR(p)) > > goto out_err; > > @@ -607,6 +609,7 @@ static int > > gss_import_v2_context(const void *p, const void *end, struct > > krb5_ctx *ctx, > > gfp_t gfp_mask) > > { > > + u64 seq_send64; > > int keylen; > > > > p = simple_get_bytes(p, end, &ctx->flags, sizeof(ctx->flags)); > > @@ -617,14 +620,15 @@ gss_import_v2_context(const void *p, const > > void *end, struct krb5_ctx *ctx, > > p = simple_get_bytes(p, end, &ctx->endtime, sizeof(ctx- > > >endtime)); > > if (IS_ERR(p)) > > goto out_err; > > - p = simple_get_bytes(p, end, &ctx->seq_send64, sizeof(ctx- > > >seq_send64)); > > + p = simple_get_bytes(p, end, &seq_send64, sizeof(seq_send64)); > > if (IS_ERR(p)) > > goto out_err; > > + atomic64_set(&ctx->seq_send64, seq_send64); > > /* set seq_send for use by "older" enctypes */ > > - ctx->seq_send = ctx->seq_send64; > > - if (ctx->seq_send64 != ctx->seq_send) { > > - dprintk("%s: seq_send64 %lx, seq_send %x overflow?\n", > > __func__, > > - (unsigned long)ctx->seq_send64, ctx->seq_send); > > + atomic_set(&ctx->seq_send, seq_send64); > > + if (seq_send64 != atomic_read(&ctx->seq_send)) { > > + dprintk("%s: seq_send64 %llx, seq_send %x overflow?\n", > > __func__, > > + seq_send64, atomic_read(&ctx->seq_send)); > > p = ERR_PTR(-EINVAL); > > goto out_err; > > } > > diff --git a/net/sunrpc/auth_gss/gss_krb5_seal.c > > b/net/sunrpc/auth_gss/gss_krb5_seal.c > > index b4adeb06660b..48fe4a591b54 100644 > > --- a/net/sunrpc/auth_gss/gss_krb5_seal.c > > +++ b/net/sunrpc/auth_gss/gss_krb5_seal.c > > @@ -123,30 +123,6 @@ setup_token_v2(struct krb5_ctx *ctx, struct > > xdr_netobj *token) > > return krb5_hdr; > > } > > > > -u32 > > -gss_seq_send_fetch_and_inc(struct krb5_ctx *ctx) > > -{ > > - u32 old, seq_send = READ_ONCE(ctx->seq_send); > > - > > - do { > > - old = seq_send; > > - seq_send = cmpxchg(&ctx->seq_send, old, old + 1); > > - } while (old != seq_send); > > - return seq_send; > > -} > > - > > -u64 > > -gss_seq_send64_fetch_and_inc(struct krb5_ctx *ctx) > > -{ > > - u64 old, seq_send = READ_ONCE(ctx->seq_send); > > - > > - do { > > - old = seq_send; > > - seq_send = cmpxchg64(&ctx->seq_send64, old, old + 1); > > - } while (old != seq_send); > > - return seq_send; > > -} > > - > > static u32 > > gss_get_mic_v1(struct krb5_ctx *ctx, struct xdr_buf *text, > > struct xdr_netobj *token) > > @@ -177,7 +153,7 @@ gss_get_mic_v1(struct krb5_ctx *ctx, struct > > xdr_buf *text, > > > > memcpy(ptr + GSS_KRB5_TOK_HDR_LEN, md5cksum.data, > > md5cksum.len); > > > > - seq_send = gss_seq_send_fetch_and_inc(ctx); > > + seq_send = atomic_fetch_inc(&ctx->seq_send); > > > > if (krb5_make_seq_num(ctx, ctx->seq, ctx->initiate ? 0 : 0xff, > > seq_send, ptr + GSS_KRB5_TOK_HDR_LEN, ptr > > + 8)) > > @@ -205,7 +181,7 @@ gss_get_mic_v2(struct krb5_ctx *ctx, struct > > xdr_buf *text, > > > > /* Set up the sequence number. Now 64-bits in clear > > * text and w/o direction indicator */ > > - seq_send_be64 = cpu_to_be64(gss_seq_send64_fetch_and_inc(ctx)); > > + seq_send_be64 = cpu_to_be64(atomic64_fetch_inc(&ctx- > > >seq_send64)); > > memcpy(krb5_hdr + 8, (char *) &seq_send_be64, 8); > > > > if (ctx->initiate) { > > diff --git a/net/sunrpc/auth_gss/gss_krb5_wrap.c > > b/net/sunrpc/auth_gss/gss_krb5_wrap.c > > index 962fa84e6db1..5cdde6cb703a 100644 > > --- a/net/sunrpc/auth_gss/gss_krb5_wrap.c > > +++ b/net/sunrpc/auth_gss/gss_krb5_wrap.c > > @@ -228,7 +228,7 @@ gss_wrap_kerberos_v1(struct krb5_ctx *kctx, int > > offset, > > > > memcpy(ptr + GSS_KRB5_TOK_HDR_LEN, md5cksum.data, > > md5cksum.len); > > > > - seq_send = gss_seq_send_fetch_and_inc(kctx); > > + seq_send = atomic_fetch_inc(&kctx->seq_send); > > > > /* XXX would probably be more efficient to compute checksum > > * and encrypt at the same time: */ > > @@ -475,7 +475,7 @@ gss_wrap_kerberos_v2(struct krb5_ctx *kctx, u32 > > offset, > > *be16ptr++ = 0; > > > > be64ptr = (__be64 *)be16ptr; > > - *be64ptr = cpu_to_be64(gss_seq_send64_fetch_and_inc(kctx)); > > + *be64ptr = cpu_to_be64(atomic64_fetch_inc(&kctx->seq_send64)); > > > > err = (*kctx->gk5e->encrypt_v2)(kctx, offset, buf, pages); > > if (err) > > -- Trond Myklebust CTO, Hammerspace Inc 4300 El Camino Real, Suite 105 Los Altos, CA 94022 www.hammer.space
