Re: [PATCH 3/3] btrfs: Avoid live-lock in search_ioctl() on hardware with sub-page faults
From: David Sterba <hidden>
Date: 2021-11-26 16:45:11
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linux-arm-kernel, linux-fsdevel, lkml
On Wed, Nov 24, 2021 at 07:20:24PM +0000, Catalin Marinas wrote:
Commit a48b73eca4ce ("btrfs: fix potential deadlock in the search
ioctl") addressed a lockdep warning by pre-faulting the user pages and
attempting the copy_to_user_nofault() in an infinite loop. On
architectures like arm64 with MTE, an access may fault within a page at
a location different from what fault_in_writeable() probed. Since the
sk_offset is rewound to the previous struct btrfs_ioctl_search_header
boundary, there is no guaranteed forward progress and search_ioctl() may
live-lock.
Use fault_in_exact_writeable() instead which probes the entire user
buffer for faults at sub-page granularity.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Al Viro <viro@zeniv.linux.org.uk>Acked-by: David Sterba <dsterba@suse.com>