Re: [PATCH] mm: prevent concurrent unmap_mapping_range() on the same inode

On Tue, 08 Feb 2011, Gurudas Pai wrote:

quoted

On Wed, 26 Jan 2011, Hugh Dickins wrote:

quoted

I had wanted to propose that for now you modify just fuse to use
i_alloc_sem for serialization there, and I provide a patch to
unmap_mapping_range() to give safety to whatever other cases there are
(I'm now sure there are other cases, but also sure that I cannot
safely identify them all and fix them correctly at source myself -
even if I found time to do the patches, they'd need at least a release
cycle to bed in with BUG_ONs).

Since fuse is the only one where the BUG has actually been triggered,
and since there are problems with all the proposed generic approaches,
I concur.  I didn't want to use i_alloc_sem here as it's more
confusing than a new mutex.

Gurudas, could you please give this patch a go in your testcase?

I found this BUG with nfs, so trying with current patch may not help.
https://lkml.org/lkml/2010/12/29/9

Let me know if I have to run this

Ahh, I was not aware of that.  No, in that case there's not much point
in trying this patch for you as it only fixes the issue in fuse. I
haven't looked at the NFS side of it yet.

Added Trond to the Cc.

Thanks,
Miklos

quoted

From: Miklos Szeredi <redacted>
Subject: fuse: prevent concurrent unmap on the same inode

Running a fuse filesystem with multiple open()'s in parallel can
trigger a "kernel BUG at mm/truncate.c:475"

The reason is, unmap_mapping_range() is not prepared for more than
one concurrent invocation per inode.

Truncate and hole punching already serialize with i_mutex.  Other
callers of unmap_mapping_range() do not, and it's difficult to get
i_mutex protection for all callers.  In particular ->d_revalidate(),
which calls invalidate_inode_pages2_range() in fuse, may be called
with or without i_mutex.

This patch adds a new mutex to fuse_inode to prevent running multiple
concurrent unmap_mapping_range() on the same mapping.

Thanks,
-Guru

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>