>
> We have tried the latest aufs (20080512) as of this morning, and
> the problem does not seem to reproduce, but I can't understand why,
> since there was no change in aufs_nopage() (though there was a
> suspicious un-comment of memory barrier in the unused aufs_fault()).
Well, the SIGBUS issue did eventually reproduce under the latest aufs
(20080512). So no magical fixes were in that patch set. ;-)
As a test, I've applied the following patch to our aufs in order to
serialize access to aufs_nopage() by taking a write lock on the
mmap_sem. 600 runs so far on this kernel without triggering the
issue. (Last test reproduced before run 300). However, I'll let the
testing run overnight.
I'm not sure if the memory barrier is still needed, especially when
the call is being serialized, but I left it in for now for symmetry
with aufs_fault():
Index: linux+rh+chaos/fs/aufs/f_op.c
===================================================================
--- linux+rh+chaos.orig/fs/aufs/f_op.c
+++ linux+rh+chaos/fs/aufs/f_op.c
@@ -411,6 +411,12 @@ static struct page *aufs_nopage(struct v
static DECLARE_WAIT_QUEUE_HEAD(wq);
struct au_finfo *finfo;
+ /*
+ * Need to get write lock as we'll update vma
+ */
+ up_read (&vma->vm_mm->mmap_sem);
+ down_write (&vma->vm_mm->mmap_sem);
+
AuTraceEnter();
AuDebugOn(!vma || !vma->vm_file);
wait_event(wq, (file = au_robr_safe_file(vma)));
@@ -425,7 +431,7 @@ static struct page *aufs_nopage(struct v
h_file = finfo->fi_hfile[0 + finfo->fi_bstart].hf_file;
AuDebugOn(!h_file || !au_test_mmapped(file));
vma->vm_file = h_file;
- //smp_mb();
+ smp_mb();
page = finfo->fi_h_vm_ops->nopage(vma, addr, type);
//file->f_ra = h_file->f_ra; //??
au_robr_reset_file(vma, file);
@@ -444,6 +450,10 @@ static struct page *aufs_nopage(struct v
//inode->i_atime = h_file->f_dentry->d_inode->i_atime;
}
AuTraceErrPtr(page);
+ /*
+ * Reassert read lock
+ */
+ downgrade_write (&vma->vm_mm->mmap_sem);
return page;
}
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