Recipe for creating unlink deadlocks

[Zygo Blaxell <ce3g8jdj@xxxxxxxxxxxxxxxxxxxxx>]

This is the simplest repro recipe for this that I have found so far.
It takes only a few minutes for the rm processes to get stuck here:

# cat /proc/28396/stack                                                                                                                                       Thu May  7 18:13:05 2015

[<ffffffff813c8a2d>] lock_extent_bits+0x1ad/0x200
[<ffffffff813b5dfa>] btrfs_evict_inode+0x17a/0x5e0
[<ffffffff8123fc68>] evict+0xb8/0x1b0
[<ffffffff81240813>] iput+0x1f3/0x260
[<ffffffff81233c68>] do_unlinkat+0x1d8/0x360
[<ffffffff812346db>] SyS_unlinkat+0x1b/0x40
[<ffffffff8190024d>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff


Run these three scripts in a directory that is the top of a subvol:

	# Script #1:  randomly create or delete snapshots
	while sleep 1; do
		if [ $[RANDOM%2] = 0 ]; then
			btrfs sub snap . snaps-$RANDOM
		else
			for x in snaps-*; do
				btrfs sub del $x
				break
			done
			btrfs sub sync .
		fi
	done 

	# Script #2:  create a bunch of files of random sizes
	while true; do
		d=$[RANDOM%9]/$[RANDOM%9]/$[RANDOM%9]/$[RANDOM%9]
		mkdir -p ${d%/*}
		head -c $[RANDOM%1024]k /usr/share/doc/chromium/copyright > $d
	done 

	# Script #3:  read and immediately delete all the files
	while date; do
		sleep 1
		find -type f -exec cat {} \; -exec rm -fv {} \; > /dev/null
	done

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