Attachment 313389 Details for Bug 457779 – please test this patch

[patch] please test this patch

z (text/plain), 1.55 KB, created by CPUShare on 2008-08-04 18:02:03 UTC

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Creator: CPUShare

Created: 2008-08-04 18:02:03 UTC

Size: 1.55 KB

patch

obsolete

>From: Andrea Arcangeli <andrea@qumranet.com>
>
>Lockdep can't recognize if spinlocks are at a different address. So
>using trylock in a loop is one way to avoid lockdep to generate false
>positives. After lockdep will be fixed this change can and should be
>reverted.
>
>Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
>---
>
>Resubmit because I didn't update the subject and so I improved the
>comments too. This is mostly to show it's a bug in lockdep and it can
>be trivially worked around without having to fix lockdep for real, any
>superior solution to this hack is more than welcome and recommended.
>
>diff -r 3469dce61df1 mm/mmap.c
>--- a/mm/mmap.c	Tue Jul 29 20:01:28 2008 +0200
>+++ b/mm/mmap.c	Mon Aug 04 19:54:27 2008 +0200
>@@ -2279,8 +2279,12 @@ static void vm_lock_anon_vma(struct anon
> 		/*
> 		 * The LSB of head.next can't change from under us
> 		 * because we hold the mm_all_locks_mutex.
>+		 *
>+		 * spin_lock would confuse lockdep who doesn't notice
>+		 * the 'anon_vma' always changing address.
> 		 */
>-		spin_lock(&anon_vma->lock);
>+		while (!spin_trylock(&anon_vma->lock))
>+			cpu_relax();
> 		/*
> 		 * We can safely modify head.next after taking the
> 		 * anon_vma->lock. If some other vma in this mm shares
>@@ -2310,7 +2314,12 @@ static void vm_lock_mapping(struct addre
> 		 */
> 		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
> 			BUG();
>-		spin_lock(&mapping->i_mmap_lock);
>+		/*
>+		 * spin_lock would confuse lockdep who doesn't notice
>+		 * the 'mapping' always changing address.
>+		 */
>+		while (!spin_trylock(&mapping->i_mmap_lock))
>+			cpu_relax();
> 	}
> }
> 
>

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Attachments on bug 457779: 313389