linux-kernel - Re: [PATCH] lib: atomic64: Initialize locks statically to fix early users

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Message-ID: <20121220190642.GE21056@atomide.com>
Date:	Thu, 20 Dec 2012 11:06:43 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
	paul@...an.com, vaibhav.bedia@...com,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] lib: atomic64: Initialize locks statically to fix
 early users

* Stephen Boyd <sboyd@...eaurora.org> [121219 23:42]:
> The atomic64 library uses a handful of static spin locks to
> implement atomic 64-bit operations on architectures without
> support for atomic 64-bit instructions. Unfortunately, the
> spinlocks are initialized in a pure initcall and that is too late
> for the vfs namespace code which wants to use atomic64 operations
> before the initcall is run (introduced by 8823c07 "vfs: Add setns
> support for the mount namespace").
> 
> This leads to BUG messages such as:
> 
> BUG: spinlock bad magic on CPU#0, swapper/0/0
>  lock: atomic64_lock+0x240/0x400, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
> [<c001af64>] (unwind_backtrace+0x0/0xf0) from [<c02c2010>] (do_raw_spin_lock+0x158/0x198)
> [<c02c2010>] (do_raw_spin_lock+0x158/0x198) from [<c04d89ec>] (_raw_spin_lock_irqsave+0x4c/0x58)
> [<c04d89ec>] (_raw_spin_lock_irqsave+0x4c/0x58) from [<c02cabf0>] (atomic64_add_return+0x30/0x5c)
> [<c02cabf0>] (atomic64_add_return+0x30/0x5c) from [<c0124564>] (alloc_mnt_ns.clone.14+0x44/0xac)
> [<c0124564>] (alloc_mnt_ns.clone.14+0x44/0xac) from [<c0124f4c>] (create_mnt_ns+0xc/0x54)
> [<c0124f4c>] (create_mnt_ns+0xc/0x54) from [<c06f31a4>] (mnt_init+0x120/0x1d4)
> [<c06f31a4>] (mnt_init+0x120/0x1d4) from [<c06f2d50>] (vfs_caches_init+0xe0/0x10c)
> [<c06f2d50>] (vfs_caches_init+0xe0/0x10c) from [<c06d4798>] (start_kernel+0x29c/0x300)
> [<c06d4798>] (start_kernel+0x29c/0x300) from [<80008078>] (0x80008078)
> 
> coming out early on during boot when spinlock debugging is enabled.
> 
> Fix this problem by initializing the spinlocks statically at
> compile time.
> 
> Reported-by: Vaibhav Bedia <vaibhav.bedia@...com>
> Tested-by: Vaibhav Bedia <vaibhav.bedia@...com>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> ---
> 
> Sorry Andrew, I couldn't find a maintainer of this file so I
> am picking on you.

Works for me:

Tested-by: Tony Lindgren <tony@...mide.com>

Added Linus, Benjamin and David to Cc as this came up on the ARM list.

 
>  lib/atomic64.c | 17 +++++------------
>  1 file changed, 5 insertions(+), 12 deletions(-)
> 
> diff --git a/lib/atomic64.c b/lib/atomic64.c
> index 9785378..08a4f06 100644
> --- a/lib/atomic64.c
> +++ b/lib/atomic64.c
> @@ -31,7 +31,11 @@
>  static union {
>  	raw_spinlock_t lock;
>  	char pad[L1_CACHE_BYTES];
> -} atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp;
> +} atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp = {
> +	[0 ... (NR_LOCKS - 1)] = {
> +		.lock =  __RAW_SPIN_LOCK_UNLOCKED(atomic64_lock.lock),
> +	},
> +};
>  
>  static inline raw_spinlock_t *lock_addr(const atomic64_t *v)
>  {
> @@ -173,14 +177,3 @@ int atomic64_add_unless(atomic64_t *v, long long a, long long u)
>  	return ret;
>  }
>  EXPORT_SYMBOL(atomic64_add_unless);
> -
> -static int init_atomic64_lock(void)
> -{
> -	int i;
> -
> -	for (i = 0; i < NR_LOCKS; ++i)
> -		raw_spin_lock_init(&atomic64_lock[i].lock);
> -	return 0;
> -}
> -
> -pure_initcall(init_atomic64_lock);
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> hosted by The Linux Foundation
> 
> --
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