On Wed, 26 Jan 2011, Hugh Dickins wrote:
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
From: Miklos Szeredi <mszeredi@xxxxxxx>
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
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