linux-stable.git/include/linux/rculist_nulls.h, branch v4.4.233

rcu: Use WRITE_ONCE() for assignments to ->pprev for hlist_nulls

2020-02-28T14:39:02+00:00

[ Upstream commit 860c8802ace14c646864795e057349c9fb2d60ad ]

Eric Dumazet supplied a KCSAN report of a bug that forces use
of hlist_unhashed_lockless() from sk_unhashed():

------------------------------------------------------------------------

BUG: KCSAN: data-race in inet_unhash / inet_unhash

write to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 1:
 __hlist_nulls_del include/linux/list_nulls.h:88 [inline]
 hlist_nulls_del_init_rcu include/linux/rculist_nulls.h:36 [inline]
 __sk_nulls_del_node_init_rcu include/net/sock.h:676 [inline]
 inet_unhash+0x38f/0x4a0 net/ipv4/inet_hashtables.c:612
 tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
 tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
 tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
 tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
 tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
 tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
 call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
 expire_timers kernel/time/timer.c:1449 [inline]
 __run_timers kernel/time/timer.c:1773 [inline]
 __run_timers kernel/time/timer.c:1740 [inline]
 run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
 arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
 default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
 cpuidle_idle_call kernel/sched/idle.c:154 [inline]
 do_idle+0x1af/0x280 kernel/sched/idle.c:263
 cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
 start_secondary+0x208/0x260 arch/x86/kernel/smpboot.c:264
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241

read to 0xffff8880a69a0170 of 8 bytes by interrupt on cpu 0:
 sk_unhashed include/net/sock.h:607 [inline]
 inet_unhash+0x3d/0x4a0 net/ipv4/inet_hashtables.c:592
 tcp_set_state+0xfa/0x3e0 net/ipv4/tcp.c:2249
 tcp_done+0x93/0x1e0 net/ipv4/tcp.c:3854
 tcp_write_err+0x7e/0xc0 net/ipv4/tcp_timer.c:56
 tcp_retransmit_timer+0x9b8/0x16d0 net/ipv4/tcp_timer.c:479
 tcp_write_timer_handler+0x42d/0x510 net/ipv4/tcp_timer.c:599
 tcp_write_timer+0xd1/0xf0 net/ipv4/tcp_timer.c:619
 call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
 expire_timers kernel/time/timer.c:1449 [inline]
 __run_timers kernel/time/timer.c:1773 [inline]
 __run_timers kernel/time/timer.c:1740 [inline]
 run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 native_safe_halt+0xe/0x10 arch/x86/kernel/paravirt.c:71
 arch_cpu_idle+0x1f/0x30 arch/x86/kernel/process.c:571
 default_idle_call+0x1e/0x40 kernel/sched/idle.c:94
 cpuidle_idle_call kernel/sched/idle.c:154 [inline]
 do_idle+0x1af/0x280 kernel/sched/idle.c:263
 cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:355
 rest_init+0xec/0xf6 init/main.c:452
 arch_call_rest_init+0x17/0x37
 start_kernel+0x838/0x85e init/main.c:786
 x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:490
 x86_64_start_kernel+0x72/0x76 arch/x86/kernel/head64.c:471
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011

------------------------------------------------------------------------

This commit therefore replaces C-language assignments with WRITE_ONCE()
in include/linux/list_nulls.h and include/linux/rculist_nulls.h.

Reported-by: Eric Dumazet  # For KCSAN
Signed-off-by: Paul E. McKenney 
Signed-off-by: Sasha Levin

net: force a reload of first item in hlist_nulls_for_each_entry_rcu

2013-06-03T03:53:59+00:00

Roman Gushchin discovered that udp4_lib_lookup2() was not reloading
first item in the rcu protected list, in case the loop was restarted.

This produced soft lockups as in https://lkml.org/lkml/2013/4/16/37

rcu_dereference(X)/ACCESS_ONCE(X) seem to not work as intended if X is
ptr->field :

In some cases, gcc caches the value or ptr->field in a register.

Use a barrier() to disallow such caching, as documented in
Documentation/atomic_ops.txt line 114

Thanks a lot to Roman for providing analysis and numerous patches.

Diagnosed-by: Roman Gushchin 
Signed-off-by: Eric Dumazet 
Reported-by: Boris Zhmurov 
Signed-off-by: Roman Gushchin 
Acked-by: Paul E. McKenney 
Signed-off-by: David S. Miller

rculist: avoid __rcu annotations

2010-08-20T00:18:00+00:00

This avoids warnings from missing __rcu annotations
in the rculist implementation, making it possible to
use the same lists in both RCU and non-RCU cases.

We can add rculist annotations later, together with
lockdep support for rculist, which is missing as well,
but that may involve changing all the users.

Signed-off-by: Arnd Bergmann 
Signed-off-by: Paul E. McKenney 
Cc: Pavel Emelyanov 
Cc: Sukadev Bhattiprolu 
Reviewed-by: Josh Triplett

rcu: Disable lockdep checking in RCU list-traversal primitives

2010-02-25T08:41:02+00:00

The theory is that use of bare rcu_dereference() is more prone
to error than use of the RCU list-traversal primitives.
Therefore, disable lockdep RCU read-side critical-section
checking in these primitives for the time being.  Once all of
the rcu_dereference() uses have been dealt with, it may be time
to re-enable lockdep checking for the RCU list-traversal
primitives.

Signed-off-by: Paul E. McKenney 
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1266887105-1528-4-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar

rcu: Fix whitespace inconsistencies

2009-09-19T06:53:22+00:00

Fix a number of whitespace ^Ierrors in the include/linux/rcu*
and the kernel/rcu* files.

Signed-off-by: Paul E. McKenney 
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
LKML-Reference: <20090918172819.GA24405@linux.vnet.ibm.com>
[ did more checkpatch fixlets ]
Signed-off-by: Ingo Molnar

rcu: Introduce hlist_nulls variant of hlist

2008-11-17T03:37:55+00:00

hlist uses NULL value to finish a chain.

hlist_nulls variant use the low order bit set to 1 to signal an end-of-list marker.

This allows to store many different end markers, so that some RCU lockless
algos (used in TCP/UDP stack for example) can save some memory barriers in
fast paths.

Two new files are added :

include/linux/list_nulls.h
  - mimics hlist part of include/linux/list.h, derived to hlist_nulls variant

include/linux/rculist_nulls.h
  - mimics hlist part of include/linux/rculist.h, derived to hlist_nulls variant

   Only four helpers are declared for the moment :

     hlist_nulls_del_init_rcu(), hlist_nulls_del_rcu(),
     hlist_nulls_add_head_rcu() and hlist_nulls_for_each_entry_rcu()

prefetches() were removed, since an end of list is not anymore NULL value.
prefetches() could trigger useless (and possibly dangerous) memory transactions.

Example of use (extracted from __udp4_lib_lookup())

	struct sock *sk, *result;
        struct hlist_nulls_node *node;
        unsigned short hnum = ntohs(dport);
        unsigned int hash = udp_hashfn(net, hnum);
        struct udp_hslot *hslot = &udptable->hash[hash];
        int score, badness;

        rcu_read_lock();
begin:
        result = NULL;
        badness = -1;
        sk_nulls_for_each_rcu(sk, node, &hslot->head) {
                score = compute_score(sk, net, saddr, hnum, sport,
                                      daddr, dport, dif);
                if (score > badness) {
                        result = sk;
                        badness = score;
                }
        }
        /*
         * if the nulls value we got at the end of this lookup is
         * not the expected one, we must restart lookup.
         * We probably met an item that was moved to another chain.
         */
        if (get_nulls_value(node) != hash)
                goto begin;

        if (result) {
                if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt)))
                        result = NULL;
                else if (unlikely(compute_score(result, net, saddr, hnum, sport,
                                  daddr, dport, dif) < badness)) {
                        sock_put(result);
                        goto begin;
                }
        }
        rcu_read_unlock();
        return result;

Signed-off-by: Eric Dumazet 
Acked-by: Peter Zijlstra 
Signed-off-by: David S. Miller