* [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire @ 2014-09-01 11:32 Shakil A Khan 2014-09-01 13:50 ` Trond Myklebust 0 siblings, 1 reply; 11+ messages in thread From: Shakil A Khan @ 2014-09-01 11:32 UTC (permalink / raw) To: linux-nfs Cc: linux-kernel, netdev, peterz, paulmck, andros, jlayton, davem, bfields, trond.myklebust, Shakil A Khan Signed-off-by : Shakil A Khan <shakilk1729@gmail.com> --- net/sunrpc/auth_gss/auth_gss.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c index afb292c..bea0951 100644 --- a/net/sunrpc/auth_gss/auth_gss.c +++ b/net/sunrpc/auth_gss/auth_gss.c @@ -1387,7 +1387,7 @@ gss_key_timeout(struct rpc_cred *rc) struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base); struct gss_cl_ctx *ctx; unsigned long now = jiffies; - unsigned long expire; + unsigned long expire = 0; rcu_read_lock(); ctx = rcu_dereference(gss_cred->gc_ctx); -- 1.7.1 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire @ 2014-09-01 13:50 ` Trond Myklebust 0 siblings, 0 replies; 11+ messages in thread From: Trond Myklebust @ 2014-09-01 13:50 UTC (permalink / raw) To: Shakil A Khan Cc: Linux NFS Mailing List, Linux Kernel mailing list, netdev, Peter Zijlstra, Paul McKenney, William Andros Adamson, Jeffrey Layton, David S. Miller, Bruce Fields On Mon, Sep 1, 2014 at 7:32 AM, Shakil A Khan <shakilk1729@gmail.com> wrote: > Signed-off-by : Shakil A Khan <shakilk1729@gmail.com> > --- > net/sunrpc/auth_gss/auth_gss.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c > index afb292c..bea0951 100644 > --- a/net/sunrpc/auth_gss/auth_gss.c > +++ b/net/sunrpc/auth_gss/auth_gss.c > @@ -1387,7 +1387,7 @@ gss_key_timeout(struct rpc_cred *rc) > struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base); > struct gss_cl_ctx *ctx; > unsigned long now = jiffies; > - unsigned long expire; > + unsigned long expire = 0; > > rcu_read_lock(); > ctx = rcu_dereference(gss_cred->gc_ctx); > -- > 1.7.1 That would be a compiler bug, not a kernel bug. The kernel code is perfectly correct as it stands, and will never access the uninitialised variable. -- Trond Myklebust Linux NFS client maintainer, PrimaryData trond.myklebust@primarydata.com ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire @ 2014-09-01 13:50 ` Trond Myklebust 0 siblings, 0 replies; 11+ messages in thread From: Trond Myklebust @ 2014-09-01 13:50 UTC (permalink / raw) To: Shakil A Khan Cc: Linux NFS Mailing List, Linux Kernel mailing list, netdev-u79uwXL29TY76Z2rM5mHXA, Peter Zijlstra, Paul McKenney, William Andros Adamson, Jeffrey Layton, David S. Miller, Bruce Fields On Mon, Sep 1, 2014 at 7:32 AM, Shakil A Khan <shakilk1729-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote: > Signed-off-by : Shakil A Khan <shakilk1729-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> > --- > net/sunrpc/auth_gss/auth_gss.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c > index afb292c..bea0951 100644 > --- a/net/sunrpc/auth_gss/auth_gss.c > +++ b/net/sunrpc/auth_gss/auth_gss.c > @@ -1387,7 +1387,7 @@ gss_key_timeout(struct rpc_cred *rc) > struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base); > struct gss_cl_ctx *ctx; > unsigned long now = jiffies; > - unsigned long expire; > + unsigned long expire = 0; > > rcu_read_lock(); > ctx = rcu_dereference(gss_cred->gc_ctx); > -- > 1.7.1 That would be a compiler bug, not a kernel bug. The kernel code is perfectly correct as it stands, and will never access the uninitialised variable. -- Trond Myklebust Linux NFS client maintainer, PrimaryData trond.myklebust-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire 2014-09-01 13:50 ` Trond Myklebust (?) @ 2014-09-02 10:52 ` Boaz Harrosh 2014-09-02 13:21 ` Bruce Fields -1 siblings, 1 reply; 11+ messages in thread From: Boaz Harrosh @ 2014-09-02 10:52 UTC (permalink / raw) To: Trond Myklebust, Shakil A Khan Cc: Linux NFS Mailing List, Linux Kernel mailing list, netdev, Peter Zijlstra, Paul McKenney, William Andros Adamson, Jeffrey Layton, David S. Miller, Bruce Fields On 09/01/2014 04:50 PM, Trond Myklebust wrote: > On Mon, Sep 1, 2014 at 7:32 AM, Shakil A Khan <shakilk1729@gmail.com> wrote: >> Signed-off-by : Shakil A Khan <shakilk1729@gmail.com> >> --- >> net/sunrpc/auth_gss/auth_gss.c | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c >> index afb292c..bea0951 100644 >> --- a/net/sunrpc/auth_gss/auth_gss.c >> +++ b/net/sunrpc/auth_gss/auth_gss.c >> @@ -1387,7 +1387,7 @@ gss_key_timeout(struct rpc_cred *rc) >> struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base); >> struct gss_cl_ctx *ctx; >> unsigned long now = jiffies; >> - unsigned long expire; >> + unsigned long expire = 0; >> >> rcu_read_lock(); >> ctx = rcu_dereference(gss_cred->gc_ctx); >> -- >> 1.7.1 > > That would be a compiler bug, not a kernel bug. The kernel code is > perfectly correct as it stands, and will never access the > uninitialised variable. > Than you will need the infamous uninitialised_var() diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c index afb292c..bea0951 100644 --- a/net/sunrpc/auth_gss/auth_gss.c +++ b/net/sunrpc/auth_gss/auth_gss.c @@ -1387,7 +1387,7 @@ gss_key_timeout(struct rpc_cred *rc) struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base); struct gss_cl_ctx *ctx; unsigned long now = jiffies; - unsigned long expire; + unsigned long uninitialised_var(expire); rcu_read_lock(); ctx = rcu_dereference(gss_cred->gc_ctx); Cheers Boaz ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire @ 2014-09-02 13:21 ` Bruce Fields 0 siblings, 0 replies; 11+ messages in thread From: Bruce Fields @ 2014-09-02 13:21 UTC (permalink / raw) To: Boaz Harrosh Cc: Trond Myklebust, Shakil A Khan, Linux NFS Mailing List, Linux Kernel mailing list, netdev, Peter Zijlstra, Paul McKenney, William Andros Adamson, Jeffrey Layton, David S. Miller On Tue, Sep 02, 2014 at 01:52:15PM +0300, Boaz Harrosh wrote: > On 09/01/2014 04:50 PM, Trond Myklebust wrote: > > On Mon, Sep 1, 2014 at 7:32 AM, Shakil A Khan <shakilk1729@gmail.com> wrote: > >> Signed-off-by : Shakil A Khan <shakilk1729@gmail.com> > >> --- > >> net/sunrpc/auth_gss/auth_gss.c | 2 +- > >> 1 files changed, 1 insertions(+), 1 deletions(-) > >> > >> diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c > >> index afb292c..bea0951 100644 > >> --- a/net/sunrpc/auth_gss/auth_gss.c > >> +++ b/net/sunrpc/auth_gss/auth_gss.c > >> @@ -1387,7 +1387,7 @@ gss_key_timeout(struct rpc_cred *rc) > >> struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base); > >> struct gss_cl_ctx *ctx; > >> unsigned long now = jiffies; > >> - unsigned long expire; > >> + unsigned long expire = 0; > >> > >> rcu_read_lock(); > >> ctx = rcu_dereference(gss_cred->gc_ctx); > >> -- > >> 1.7.1 > > > > That would be a compiler bug, not a kernel bug. The kernel code is > > perfectly correct as it stands, and will never access the > > uninitialised variable. > > > > Than you will need the infamous uninitialised_var() You'd rather avoid sprinkling that all over, though. If nothing else it increases the chances you'll suppress a legimate warning some day. And unless I'm missing something this one really does look like an unambiguous compiler bug. --b. > > diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c > index afb292c..bea0951 100644 > --- a/net/sunrpc/auth_gss/auth_gss.c > +++ b/net/sunrpc/auth_gss/auth_gss.c > @@ -1387,7 +1387,7 @@ gss_key_timeout(struct rpc_cred *rc) > struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base); > struct gss_cl_ctx *ctx; > unsigned long now = jiffies; > - unsigned long expire; > + unsigned long uninitialised_var(expire); > > rcu_read_lock(); > ctx = rcu_dereference(gss_cred->gc_ctx); > > Cheers > Boaz ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire @ 2014-09-02 13:21 ` Bruce Fields 0 siblings, 0 replies; 11+ messages in thread From: Bruce Fields @ 2014-09-02 13:21 UTC (permalink / raw) To: Boaz Harrosh Cc: Trond Myklebust, Shakil A Khan, Linux NFS Mailing List, Linux Kernel mailing list, netdev-u79uwXL29TY76Z2rM5mHXA, Peter Zijlstra, Paul McKenney, William Andros Adamson, Jeffrey Layton, David S. Miller On Tue, Sep 02, 2014 at 01:52:15PM +0300, Boaz Harrosh wrote: > On 09/01/2014 04:50 PM, Trond Myklebust wrote: > > On Mon, Sep 1, 2014 at 7:32 AM, Shakil A Khan <shakilk1729-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote: > >> Signed-off-by : Shakil A Khan <shakilk1729-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> > >> --- > >> net/sunrpc/auth_gss/auth_gss.c | 2 +- > >> 1 files changed, 1 insertions(+), 1 deletions(-) > >> > >> diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c > >> index afb292c..bea0951 100644 > >> --- a/net/sunrpc/auth_gss/auth_gss.c > >> +++ b/net/sunrpc/auth_gss/auth_gss.c > >> @@ -1387,7 +1387,7 @@ gss_key_timeout(struct rpc_cred *rc) > >> struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base); > >> struct gss_cl_ctx *ctx; > >> unsigned long now = jiffies; > >> - unsigned long expire; > >> + unsigned long expire = 0; > >> > >> rcu_read_lock(); > >> ctx = rcu_dereference(gss_cred->gc_ctx); > >> -- > >> 1.7.1 > > > > That would be a compiler bug, not a kernel bug. The kernel code is > > perfectly correct as it stands, and will never access the > > uninitialised variable. > > > > Than you will need the infamous uninitialised_var() You'd rather avoid sprinkling that all over, though. If nothing else it increases the chances you'll suppress a legimate warning some day. And unless I'm missing something this one really does look like an unambiguous compiler bug. --b. > > diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c > index afb292c..bea0951 100644 > --- a/net/sunrpc/auth_gss/auth_gss.c > +++ b/net/sunrpc/auth_gss/auth_gss.c > @@ -1387,7 +1387,7 @@ gss_key_timeout(struct rpc_cred *rc) > struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base); > struct gss_cl_ctx *ctx; > unsigned long now = jiffies; > - unsigned long expire; > + unsigned long uninitialised_var(expire); > > rcu_read_lock(); > ctx = rcu_dereference(gss_cred->gc_ctx); > > Cheers > Boaz -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire @ 2014-09-02 13:59 ` Boaz Harrosh 0 siblings, 0 replies; 11+ messages in thread From: Boaz Harrosh @ 2014-09-02 13:59 UTC (permalink / raw) To: Bruce Fields Cc: Trond Myklebust, Shakil A Khan, Linux NFS Mailing List, Linux Kernel mailing list, netdev, Peter Zijlstra, Paul McKenney, William Andros Adamson, Jeffrey Layton, David S. Miller On 09/02/2014 04:21 PM, Bruce Fields wrote: > > You'd rather avoid sprinkling that all over, though. If nothing else it > increases the chances you'll suppress a legimate warning some day. > But this is exactly why it was created. If you do the "= 0" then it is gone forever. If you have missed a legitimate needed assignment, it will be missed as well. But if you do the uninitialized_var() dance then there is a make option that turns it off and every once in a while people do a make with it to see if it still holds. The diff between foo = 0; and uninitialized_var(foo) is that the programmer is communicating to his friends that: "I have encountered a bogus compiler, this is falsely initialized" As opposed to =0 the compiler bug is covered up and forgotten > And unless I'm missing something this one really does look like an > unambiguous compiler bug. > Right! so that is how you specify this in code at Linux: uninitialized_var(foo); Putting =0 is way way worse, because it will never be revised and specially not automatically with a make switch. And leaving the warning on is even worse because two three of these and people start to ignore warnings. > --b. > uninitialized_var was made to be a friend not an enemy, in the face of real ugliness it is the best we can do. And that is what it should communicate to everyone. Why has it become everyone's favorite blasphemy I do not know. Cheers Boaz ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire @ 2014-09-02 13:59 ` Boaz Harrosh 0 siblings, 0 replies; 11+ messages in thread From: Boaz Harrosh @ 2014-09-02 13:59 UTC (permalink / raw) To: Bruce Fields Cc: Trond Myklebust, Shakil A Khan, Linux NFS Mailing List, Linux Kernel mailing list, netdev-u79uwXL29TY76Z2rM5mHXA, Peter Zijlstra, Paul McKenney, William Andros Adamson, Jeffrey Layton, David S. Miller On 09/02/2014 04:21 PM, Bruce Fields wrote: > > You'd rather avoid sprinkling that all over, though. If nothing else it > increases the chances you'll suppress a legimate warning some day. > But this is exactly why it was created. If you do the "= 0" then it is gone forever. If you have missed a legitimate needed assignment, it will be missed as well. But if you do the uninitialized_var() dance then there is a make option that turns it off and every once in a while people do a make with it to see if it still holds. The diff between foo = 0; and uninitialized_var(foo) is that the programmer is communicating to his friends that: "I have encountered a bogus compiler, this is falsely initialized" As opposed to =0 the compiler bug is covered up and forgotten > And unless I'm missing something this one really does look like an > unambiguous compiler bug. > Right! so that is how you specify this in code at Linux: uninitialized_var(foo); Putting =0 is way way worse, because it will never be revised and specially not automatically with a make switch. And leaving the warning on is even worse because two three of these and people start to ignore warnings. > --b. > uninitialized_var was made to be a friend not an enemy, in the face of real ugliness it is the best we can do. And that is what it should communicate to everyone. Why has it become everyone's favorite blasphemy I do not know. Cheers Boaz -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire @ 2014-09-02 14:17 ` Bruce Fields 0 siblings, 0 replies; 11+ messages in thread From: Bruce Fields @ 2014-09-02 14:17 UTC (permalink / raw) To: Boaz Harrosh Cc: Trond Myklebust, Shakil A Khan, Linux NFS Mailing List, Linux Kernel mailing list, netdev, Peter Zijlstra, Paul McKenney, William Andros Adamson, Jeffrey Layton, David S. Miller On Tue, Sep 02, 2014 at 04:59:45PM +0300, Boaz Harrosh wrote: > uninitialized_var was made to be a friend not an enemy, in the face of real > ugliness it is the best we can do. And that is what it should communicate to > everyone. Why has it become everyone's favorite blasphemy I do not know. Not personally claiming it should never be used, just that this particular case is kind of extreme, since unless I'm missing a real compilication it's basically just: if (ctx) assign to expire ... if (ctx) use expire A compiler wouldn't have to be that smart to actually prove to itself that expire is initialized at the last step, and that it's not only failing to do that but actually flagging it as possibly unitialized is weird. --b. ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire @ 2014-09-02 14:17 ` Bruce Fields 0 siblings, 0 replies; 11+ messages in thread From: Bruce Fields @ 2014-09-02 14:17 UTC (permalink / raw) To: Boaz Harrosh Cc: Trond Myklebust, Shakil A Khan, Linux NFS Mailing List, Linux Kernel mailing list, netdev-u79uwXL29TY76Z2rM5mHXA, Peter Zijlstra, Paul McKenney, William Andros Adamson, Jeffrey Layton, David S. Miller On Tue, Sep 02, 2014 at 04:59:45PM +0300, Boaz Harrosh wrote: > uninitialized_var was made to be a friend not an enemy, in the face of real > ugliness it is the best we can do. And that is what it should communicate to > everyone. Why has it become everyone's favorite blasphemy I do not know. Not personally claiming it should never be used, just that this particular case is kind of extreme, since unless I'm missing a real compilication it's basically just: if (ctx) assign to expire ... if (ctx) use expire A compiler wouldn't have to be that smart to actually prove to itself that expire is initialized at the last step, and that it's not only failing to do that but actually flagging it as possibly unitialized is weird. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire 2014-09-02 14:17 ` Bruce Fields (?) @ 2014-09-02 16:05 ` Boaz Harrosh -1 siblings, 0 replies; 11+ messages in thread From: Boaz Harrosh @ 2014-09-02 16:05 UTC (permalink / raw) To: Bruce Fields Cc: Trond Myklebust, Shakil A Khan, Linux NFS Mailing List, Linux Kernel mailing list, netdev, Peter Zijlstra, Paul McKenney, William Andros Adamson, Jeffrey Layton, David S. Miller On 09/02/2014 05:17 PM, Bruce Fields wrote: > On Tue, Sep 02, 2014 at 04:59:45PM +0300, Boaz Harrosh wrote: >> uninitialized_var was made to be a friend not an enemy, in the face of real >> ugliness it is the best we can do. And that is what it should communicate to >> everyone. Why has it become everyone's favorite blasphemy I do not know. > > Not personally claiming it should never be used, just that this > particular case is kind of extreme, since unless I'm missing a real > compilication it's basically just: > > if (ctx) > assign to expire > ... > if (ctx) > use expire > > A compiler wouldn't have to be that smart to actually prove to itself > that expire is initialized at the last step, and that it's not only > failing to do that but actually flagging it as possibly unitialized is > weird. Actually that is a complicated case for a compiler. Because of the two different scopes. I think it only optimizes that on higher optimization values. Cross scope analysis is not done at parsing time but more on code generation time, the "warning" is more of the former phase. Perhaps change the code, if possible, so the assign and use of "expire" is under the last if (or the first)? That would be also easier on the reader. BTW: You are most probably right though, because here I do not have this problem. I guess it is the case of an old compiler with a certain compilation environment. Thanks Boaz > > --b. > ^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2014-09-02 16:05 UTC | newest] Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2014-09-01 11:32 [PATCH] Next branch: authgss: authgss.c: Fix warnings for uninitizlized variable expire Shakil A Khan 2014-09-01 13:50 ` Trond Myklebust 2014-09-01 13:50 ` Trond Myklebust 2014-09-02 10:52 ` Boaz Harrosh 2014-09-02 13:21 ` Bruce Fields 2014-09-02 13:21 ` Bruce Fields 2014-09-02 13:59 ` Boaz Harrosh 2014-09-02 13:59 ` Boaz Harrosh 2014-09-02 14:17 ` Bruce Fields 2014-09-02 14:17 ` Bruce Fields 2014-09-02 16:05 ` Boaz Harrosh
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