format stress test failure: bt_discard.c, 56: !__wt_page_is_modified(page)

############################################

#  RUN PARAMETERS

############################################

auto_throttle=1

firstfit=1

bitcnt=3

bloom=1

bloom_bit_count=10

bloom_hash_count=24

bloom_oldest=1

cache=15

checkpoints=1

checksum=uncompressed

chunk_size=7

compaction=0

compression=zlib

data_extend=0

data_source=file

delete_pct=22

dictionary=0

evict_max=0

file_type=row-store

backups=0

huffman_key=0

huffman_value=0

insert_pct=13

internal_key_truncation=1

internal_page_max=9

isolation=read-committed

key_gap=14

key_max=256

key_min=256

leak_memory=0

leaf_page_max=9

logging=0

merge_max=4

merge_threads=3

mmap=1

ops=100000

prefix_compression=1

prefix_compression_min=3

repeat_data_pct=7

reverse=0

rows=100000

runs=100

split_pct=72

statistics=0

threads=13

value_max=2638

value_min=10

wiredtiger_config=

write_pct=36

############################################

T 12: main, sleeping

T 11: eviction server, the failing thread

T 10: sweep server, sleeping

T 3, 4, 5, 6, 7, 8, 9: worker threads, trying to do a named checkpoint and waiting  on format's hot-backup lock

T 2: doing a named checkpoint and trying to clear the tree's current eviction point

T 1: starting a transaction and doing a cache-full check, waiting to find a page on the eviction queue to evict.

WT-4  0x00000000004da528 in __wt_abort (session=0x803035280) at src/os_posix/os_abort.c:21

WT-5  0x0000000000459e3c in __wt_assert (session=0x803035280, error=0, file_name=0x531580 "src/btree/bt_discard.c", 

    line_number=56, fmt=0x522129 "%s") at src/support/err.c:452

WT-6  0x00000000004f5077 in __wt_page_out (session=0x803035280, pagep=0x807f293a0) at src/btree/bt_discard.c:56

WT-7  0x00000000004f4fff in __wt_ref_out (session=0x803035280, ref=0x807f293a0) at src/btree/bt_discard.c:32

WT-8  0x0000000000489898 in __rec_page_dirty_update (session=0x803035280, ref=0x807f293a0, exclusive=0)

    at src/btree/rec_evict.c:164

WT-9  0x0000000000488c0e in __wt_rec_evict (session=0x803035280, ref=0x807f293a0, exclusive=0) at src/btree/rec_evict.c:88

WT-10 0x0000000000473e6c in __wt_evict_page (session=0x803035280, ref=0x807f293a0) at src/btree/bt_evict.c:616

WT-11 0x0000000000474403 in __wt_evict_lru_page (session=0x803035280, is_app=0) at src/btree/bt_evict.c:1218

WT-12 0x0000000000474e12 in __evict_lru_pages (session=0x803035280, is_app=0) at src/btree/bt_evict.c:701

WT-13 0x0000000000475879 in __evict_lru (session=0x803035280, flags=3) at src/btree/bt_evict.c:794

WT-14 0x000000000047514c in __evict_pass (session=0x803035280) at src/btree/bt_evict.c:484

WT-15 0x000000000047352f in __evict_server (arg=0x803035280) at src/btree/bt_evict.c:162

and we're attempting to discard a dirty page:

52		/*

53		 * We should never discard a dirty page, the file's current eviction

54		 * point or a page queued for LRU eviction.

55		 */

56		WT_ASSERT(session, !__wt_page_is_modified(page));

57		WT_ASSERT(session, !F_ISSET_ATOMIC(page, WT_PAGE_EVICT_LRU));

58		WT_ASSERT(session, !F_ISSET_ATOMIC(page, WT_PAGE_SPLITTING));

and it's empty:

(gdb) p *page 

$4 = {u = {intl = {recno = 34466205048, parent_ref = 0x8065c10e8, __index = 0x0}, row = {d = 0x806588d78, ins = 0x8065c10e8, 

      upd = 0x0, entries = 0}, col_fix = {recno = 34466205048, bitf = 0x8065c10e8 "", entries = 0}, col_var = {

      recno = 34466205048, d = 0x8065c10e8, repeats = 0x0, nrepeats = 0, entries = 0}}, dsk = 0x0, modify = 0x806597520, 

  read_gen = 130743, memory_footprint = 3195, type = 7 '\a', flags_atomic = 0 '\0'}

(gdb) p *page->modify

$6 = {disk_snap_min = 0, rec_max_txn = 0, first_dirty_txn = 91156, update_txn = 91156, bytes_dirty = 3195, u1 = {replace = {

      addr = 0x0, size = 0 '\0', type = 2 '\002', reuse = 0 '\0'}, m = {multi = 0x0, multi_entries = 512}}, u2 = {intl = {

      root_split = 0x0, split_txn = 0}, leaf = {append = 0x0, update = 0x0}}, ovfl_track = 0x807704b00, write_gen = 1, 

  page_lock = 2 '\002', flags = 1 '\001'}

but there's one element on the page's insert list:

0x806588d30: row-store leaf

        disk 0x0, entries 0, dirty, empty, write generation=1

        insert {0000078100.00/opqrstuvwxyzabcdefghijklmnop ... }

        value {0000078100/LMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQR ... }

(gdb) skip_insert_single page->u.row.ins 0

... printing level 0

$12 = {upd = 0x8067e2800,

u = {recno = 1099511627800, key = {offset = 24, size = 256}}, next = 0x80670d990}

(gdb) p *$12.upd

$13 = {txnid = 91156, next = 0x0, size = 2407}