Re: [PATCH 2/3] kernel/SRCU: provide a static initializer

From: Paul E. McKenney
Date: Tue Apr 16 2013 - 14:21:39 EST

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On Fri, Apr 12, 2013 at 10:56:27AM +0800, Lai Jiangshan wrote:
> On 04/12/2013 01:04 AM, Sebastian Andrzej Siewior wrote:
> > * Lai Jiangshan | 2013-04-09 09:09:56 [+0800]:
> >
> >> If the percpu array can be defined in __SRCU_STRUCT_INIT(),
> >> I'm happy to expose it. but it is not currently.
> >
> > I have no idea how to achieve this.
> >
> >> Why crypto can't use boot time initialization?
> >
> > It would require something like this:
> > --- linux-stable.orig/crypto/Kconfig
> > +++ linux-stable/crypto/Kconfig
> > @@ -13,7 +13,7 @@ source "crypto/async_tx/Kconfig"
> > # Cryptographic API Configuration
> > #
> > menuconfig CRYPTO
> > - tristate "Cryptographic API"
> > + bool "Cryptographic API"
> > help
> > This option provides the core Cryptographic API.
>
> Why convert to "bool"?
> srcu_init_notifier_head() can be called in module-load-time.
>
> >
> > --- linux-stable.orig/crypto/api.c
> > +++ linux-stable/crypto/api.c
> > @@ -34,6 +34,13 @@ EXPORT_SYMBOL_GPL(crypto_alg_sem);
> > struct srcu_notifier_head crypto_chain;
> > EXPORT_SYMBOL_GPL(crypto_chain);
> >
> > +static int __init crypto_api_init(void)
> > +{
> > + srcu_init_notifier_head(&crypto_chain);
> > + return 0;
> > +}
> > +core_initcall(crypto_api_init);
> > +
> > static inline struct crypto_alg *crypto_alg_get(struct crypto_alg *alg)
> > {
> > atomic_inc(&alg->cra_refcnt);
>
> And again, why crypto can't use boot time nor module-load-time initialization?

Hello, Lai,

I believe that Sebastian's point is that compile-time initialization
would be easier to use and would reduce the amount of code that must
be written, reviewed, and executed.

Thanx, Paul

> > and there is no need for this.
> >
> >>> Do you have any idea how I could get it done without this? Do you want
> >>> to move/merge header files?
> >>
> >> if crypto has to use static initialization, I will find out some way
> >> or use your patch.
> >
> > The crypto would like this:
> >
> > Subject: crypto: Convert crypto notifier chain to SRCU
> > From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Date: Fri, 05 Oct 2012 09:03:24 +0100
> >
> > The crypto notifier deadlocks on RT. Though this can be a real deadlock
> > on mainline as well due to fifo fair rwsems.
> >
> > The involved parties here are:
> >
> > [ 82.172678] swapper/0 S 0000000000000001 0 1 0 0x00000000
> > [ 82.172682] ffff88042f18fcf0 0000000000000046 ffff88042f18fc80 ffffffff81491238
> > [ 82.172685] 0000000000011cc0 0000000000011cc0 ffff88042f18c040 ffff88042f18ffd8
> > [ 82.172688] 0000000000011cc0 0000000000011cc0 ffff88042f18ffd8 0000000000011cc0
> > [ 82.172689] Call Trace:
> > [ 82.172697] [<ffffffff81491238>] ? _raw_spin_unlock_irqrestore+0x6c/0x7a
> > [ 82.172701] [<ffffffff8148fd3f>] schedule+0x64/0x66
> > [ 82.172704] [<ffffffff8148ec6b>] schedule_timeout+0x27/0xd0
> > [ 82.172708] [<ffffffff81043c0c>] ? unpin_current_cpu+0x1a/0x6c
> > [ 82.172713] [<ffffffff8106e491>] ? migrate_enable+0x12f/0x141
> > [ 82.172716] [<ffffffff8148fbbd>] wait_for_common+0xbb/0x11f
> > [ 82.172719] [<ffffffff810709f2>] ? try_to_wake_up+0x182/0x182
> > [ 82.172722] [<ffffffff8148fc96>] wait_for_completion_interruptible+0x1d/0x2e
> > [ 82.172726] [<ffffffff811debfd>] crypto_wait_for_test+0x49/0x6b
> > [ 82.172728] [<ffffffff811ded32>] crypto_register_alg+0x53/0x5a
> > [ 82.172730] [<ffffffff811ded6c>] crypto_register_algs+0x33/0x72
> > [ 82.172734] [<ffffffff81ad7686>] ? aes_init+0x12/0x12
> > [ 82.172737] [<ffffffff81ad76ea>] aesni_init+0x64/0x66
> > [ 82.172741] [<ffffffff81000318>] do_one_initcall+0x7f/0x13b
> > [ 82.172744] [<ffffffff81ac4d34>] kernel_init+0x199/0x22c
> > [ 82.172747] [<ffffffff81ac44ef>] ? loglevel+0x31/0x31
> > [ 82.172752] [<ffffffff814987c4>] kernel_thread_helper+0x4/0x10
> > [ 82.172755] [<ffffffff81491574>] ? retint_restore_args+0x13/0x13
> > [ 82.172759] [<ffffffff81ac4b9b>] ? start_kernel+0x3ca/0x3ca
> > [ 82.172761] [<ffffffff814987c0>] ? gs_change+0x13/0x13
> >
> > [ 82.174186] cryptomgr_test S 0000000000000001 0 41 2 0x00000000
> > [ 82.174189] ffff88042c971980 0000000000000046 ffffffff81d74830 0000000000000292
> > [ 82.174192] 0000000000011cc0 0000000000011cc0 ffff88042c96eb80 ffff88042c971fd8
> > [ 82.174195] 0000000000011cc0 0000000000011cc0 ffff88042c971fd8 0000000000011cc0
> > [ 82.174195] Call Trace:
> > [ 82.174198] [<ffffffff8148fd3f>] schedule+0x64/0x66
> > [ 82.174201] [<ffffffff8148ec6b>] schedule_timeout+0x27/0xd0
> > [ 82.174204] [<ffffffff81043c0c>] ? unpin_current_cpu+0x1a/0x6c
> > [ 82.174206] [<ffffffff8106e491>] ? migrate_enable+0x12f/0x141
> > [ 82.174209] [<ffffffff8148fbbd>] wait_for_common+0xbb/0x11f
> > [ 82.174212] [<ffffffff810709f2>] ? try_to_wake_up+0x182/0x182
> > [ 82.174215] [<ffffffff8148fc96>] wait_for_completion_interruptible+0x1d/0x2e
> > [ 82.174218] [<ffffffff811e4883>] cryptomgr_notify+0x280/0x385
> > [ 82.174221] [<ffffffff814943de>] notifier_call_chain+0x6b/0x98
> > [ 82.174224] [<ffffffff8108a11c>] ? rt_down_read+0x10/0x12
> > [ 82.174227] [<ffffffff810677cd>] __blocking_notifier_call_chain+0x70/0x8d
> > [ 82.174230] [<ffffffff810677fe>] blocking_notifier_call_chain+0x14/0x16
> > [ 82.174234] [<ffffffff811dd272>] crypto_probing_notify+0x24/0x50
> > [ 82.174236] [<ffffffff811dd7a1>] crypto_alg_mod_lookup+0x3e/0x74
> > [ 82.174238] [<ffffffff811dd949>] crypto_alloc_base+0x36/0x8f
> > [ 82.174241] [<ffffffff811e9408>] cryptd_alloc_ablkcipher+0x6e/0xb5
> > [ 82.174243] [<ffffffff811dd591>] ? kzalloc.clone.5+0xe/0x10
> > [ 82.174246] [<ffffffff8103085d>] ablk_init_common+0x1d/0x38
> > [ 82.174249] [<ffffffff8103852a>] ablk_ecb_init+0x15/0x17
> > [ 82.174251] [<ffffffff811dd8c6>] __crypto_alloc_tfm+0xc7/0x114
> > [ 82.174254] [<ffffffff811e0caa>] ? crypto_lookup_skcipher+0x1f/0xe4
> > [ 82.174256] [<ffffffff811e0dcf>] crypto_alloc_ablkcipher+0x60/0xa5
> > [ 82.174258] [<ffffffff811e5bde>] alg_test_skcipher+0x24/0x9b
> > [ 82.174261] [<ffffffff8106d96d>] ? finish_task_switch+0x3f/0xfa
> > [ 82.174263] [<ffffffff811e6b8e>] alg_test+0x16f/0x1d7
> > [ 82.174267] [<ffffffff811e45ac>] ? cryptomgr_probe+0xac/0xac
> > [ 82.174269] [<ffffffff811e45d8>] cryptomgr_test+0x2c/0x47
> > [ 82.174272] [<ffffffff81061161>] kthread+0x7e/0x86
> > [ 82.174275] [<ffffffff8106d9dd>] ? finish_task_switch+0xaf/0xfa
> > [ 82.174278] [<ffffffff814987c4>] kernel_thread_helper+0x4/0x10
> > [ 82.174281] [<ffffffff81491574>] ? retint_restore_args+0x13/0x13
> > [ 82.174284] [<ffffffff810610e3>] ? __init_kthread_worker+0x8c/0x8c
> > [ 82.174287] [<ffffffff814987c0>] ? gs_change+0x13/0x13
> >
> > [ 82.174329] cryptomgr_probe D 0000000000000002 0 47 2 0x00000000
> > [ 82.174332] ffff88042c991b70 0000000000000046 ffff88042c991bb0 0000000000000006
> > [ 82.174335] 0000000000011cc0 0000000000011cc0 ffff88042c98ed00 ffff88042c991fd8
> > [ 82.174338] 0000000000011cc0 0000000000011cc0 ffff88042c991fd8 0000000000011cc0
> > [ 82.174338] Call Trace:
> > [ 82.174342] [<ffffffff8148fd3f>] schedule+0x64/0x66
> > [ 82.174344] [<ffffffff814901ad>] __rt_mutex_slowlock+0x85/0xbe
> > [ 82.174347] [<ffffffff814902d2>] rt_mutex_slowlock+0xec/0x159
> > [ 82.174351] [<ffffffff81089c4d>] rt_mutex_fastlock.clone.8+0x29/0x2f
> > [ 82.174353] [<ffffffff81490372>] rt_mutex_lock+0x33/0x37
> > [ 82.174356] [<ffffffff8108a0f2>] __rt_down_read+0x50/0x5a
> > [ 82.174358] [<ffffffff8108a11c>] ? rt_down_read+0x10/0x12
> > [ 82.174360] [<ffffffff8108a11c>] rt_down_read+0x10/0x12
> > [ 82.174363] [<ffffffff810677b5>] __blocking_notifier_call_chain+0x58/0x8d
> > [ 82.174366] [<ffffffff810677fe>] blocking_notifier_call_chain+0x14/0x16
> > [ 82.174369] [<ffffffff811dd272>] crypto_probing_notify+0x24/0x50
> > [ 82.174372] [<ffffffff811debd6>] crypto_wait_for_test+0x22/0x6b
> > [ 82.174374] [<ffffffff811decd3>] crypto_register_instance+0xb4/0xc0
> > [ 82.174377] [<ffffffff811e9b76>] cryptd_create+0x378/0x3b6
> > [ 82.174379] [<ffffffff811de512>] ? __crypto_lookup_template+0x5b/0x63
> > [ 82.174382] [<ffffffff811e4545>] cryptomgr_probe+0x45/0xac
> > [ 82.174385] [<ffffffff811e4500>] ? crypto_alloc_pcomp+0x1b/0x1b
> > [ 82.174388] [<ffffffff81061161>] kthread+0x7e/0x86
> > [ 82.174391] [<ffffffff8106d9dd>] ? finish_task_switch+0xaf/0xfa
> > [ 82.174394] [<ffffffff814987c4>] kernel_thread_helper+0x4/0x10
> > [ 82.174398] [<ffffffff81491574>] ? retint_restore_args+0x13/0x13
> > [ 82.174401] [<ffffffff810610e3>] ? __init_kthread_worker+0x8c/0x8c
> > [ 82.174403] [<ffffffff814987c0>] ? gs_change+0x13/0x13
> >
> > cryptomgr_test spawns the cryptomgr_probe thread from the notifier
> > call. The probe thread fires the same notifier as the test thread and
> > deadlocks on the rwsem on RT.
> >
> > Now this is a potential deadlock in mainline as well, because we have
> > fifo fair rwsems. If another thread blocks with a down_write() on the
> > notifier chain before the probe thread issues the down_read() it will
> > block the probe thread and the whole party is dead locked.
> >
> > Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > ---
> > crypto/algapi.c | 4 ++--
> > crypto/api.c | 6 +++---
> > crypto/internal.h | 4 ++--
> > 3 files changed, 7 insertions(+), 7 deletions(-)
> >
> > --- a/crypto/algapi.c
> > +++ b/crypto/algapi.c
> > @@ -683,13 +683,13 @@ EXPORT_SYMBOL_GPL(crypto_spawn_tfm2);
> >
> > int crypto_register_notifier(struct notifier_block *nb)
> > {
> > - return blocking_notifier_chain_register(&crypto_chain, nb);
> > + return srcu_notifier_chain_register(&crypto_chain, nb);
> > }
> > EXPORT_SYMBOL_GPL(crypto_register_notifier);
> >
> > int crypto_unregister_notifier(struct notifier_block *nb)
> > {
> > - return blocking_notifier_chain_unregister(&crypto_chain, nb);
> > + return srcu_notifier_chain_unregister(&crypto_chain, nb);
> > }
> > EXPORT_SYMBOL_GPL(crypto_unregister_notifier);
> >
> > --- a/crypto/api.c
> > +++ b/crypto/api.c
> > @@ -31,7 +31,7 @@ EXPORT_SYMBOL_GPL(crypto_alg_list);
> > DECLARE_RWSEM(crypto_alg_sem);
> > EXPORT_SYMBOL_GPL(crypto_alg_sem);
> >
> > -BLOCKING_NOTIFIER_HEAD(crypto_chain);
> > +SRCU_NOTIFIER_HEAD(crypto_chain);
> > EXPORT_SYMBOL_GPL(crypto_chain);
> >
> > static inline struct crypto_alg *crypto_alg_get(struct crypto_alg *alg)
> > @@ -237,10 +237,10 @@ int crypto_probing_notify(unsigned long
> > {
> > int ok;
> >
> > - ok = blocking_notifier_call_chain(&crypto_chain, val, v);
> > + ok = srcu_notifier_call_chain(&crypto_chain, val, v);
> > if (ok == NOTIFY_DONE) {
> > request_module("cryptomgr");
> > - ok = blocking_notifier_call_chain(&crypto_chain, val, v);
> > + ok = srcu_notifier_call_chain(&crypto_chain, val, v);
> > }
> >
> > return ok;
> > --- a/crypto/internal.h
> > +++ b/crypto/internal.h
> > @@ -48,7 +48,7 @@ struct crypto_larval {
> >
> > extern struct list_head crypto_alg_list;
> > extern struct rw_semaphore crypto_alg_sem;
> > -extern struct blocking_notifier_head crypto_chain;
> > +extern struct srcu_notifier_head crypto_chain;
> >
> > #ifdef CONFIG_PROC_FS
> > void __init crypto_init_proc(void);
> > @@ -136,7 +136,7 @@ static inline int crypto_is_moribund(str
> >
> > static inline void crypto_notify(unsigned long val, void *v)
> > {
> > - blocking_notifier_call_chain(&crypto_chain, val, v);
> > + srcu_notifier_call_chain(&crypto_chain, val, v);
> > }
> >
> > #endif /* _CRYPTO_INTERNAL_H */
> >
> >> Thanks,
> >> Lai
> >
> > Sebastian
> >
>

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