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SubjectRe: [PATCH] mm: prevent concurrent unmap_mapping_range() on the same inode
On Thu, Jan 20, 2011 at 01:30:58PM +0100, Miklos Szeredi wrote:
> From: Miklos Szeredi <>
> 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. For example:
> thread1: going through a big range, stops in the middle of a vma and
> stores the restart address in vm_truncate_count.
> thread2: comes in with a small (e.g. single page) unmap request on
> the same vma, somewhere before restart_address, finds that the
> vma was already unmapped up to the restart address and happily
> returns without doing anything.
> Another scenario would be two big unmap requests, both having to
> restart the unmapping and each one setting vm_truncate_count to its
> own value. This could go on forever without any of them being able to
> finish.
> 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.

Which I think is mostly a fuse problem. I really hate bloating the
generic inode (into which the address_space is embedded) with another
mutex for deficits in rather special case filesystems.

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