Hello Maxim, thanks alot for your help. I'll try to reproduce it.

(gdb) fr 0
#0 0x000000000042cbe8 in ngx_readv_chain (c=0x2b508a1d43d0, chain=0x602348) at src/os/unix/ngx_readv_chain.c:195
195 src/os/unix/ngx_readv_chain.c: No such file or directory.
in src/os/unix/ngx_readv_chain.c

(gdb) p *chain->buf
$6 = {pos = 0x0, last = 0x0, file_pos = 0, file_last = 0, start = 0x0, end = 0x0, tag = 0x5c8480, file = 0x0, shadow = 0x0, temporary = 1, memory = 0, mmap = 0, recycled = 1, in_file = 0,
flush = 0, sync = 0, last_buf = 0, last_in_chain = 0, last_shadow = 0, temp_file = 0, num = 0}

(gdb) p *chain->next
$7 = {buf = 0x7523d8, next = 0x752638}

(gdb) p *chain->next->buf
$8 = {pos = 0x0, last = 0x0, file_pos = 0, file_last = 0, start = 0x0, end = 0x0, tag = 0x5c8480, file = 0x0, shadow = 0x0, temporary = 1, memory = 0, mmap = 0, recycled = 1, in_file = 0,
flush = 0, sync = 0, last_buf = 0, last_in_chain = 0, last_shadow = 0, temp_file = 0, num = 0}

(gdb) p *chain->next->next
$9 = {buf = 0x746ff8, next = 0x0}

(gdb) p *chain->next->next->buf
$10 = {
pos = 0x2b50cc843010 "¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î"...,
last = 0x2b50cc843010 "¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î"..., file_pos = 0, file_last = 0,
start = 0x2b50cc843010 "¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î"..., end = 0x2b50cc883010 "", tag = 0x5c8480, file = 0x0, shadow = 0x0, temporary = 1, memory = 0, mmap = 0, recycled = 1, in_file = 0, flush = 0, sync = 0,
last_buf = 0, last_in_chain = 0, last_shadow = 0, temp_file = 0, num = 2}

(gdb) p *chain->next->next->next
Cannot access memory at address 0x0
(gdb) p *chain->next->next->next->buf
Cannot access memory at address 0x0


____________________________________________

(gdb) fr 1
#1 0x000000000042b133 in ngx_event_pipe (p=0x747170, do_write=<value optimized out>) at src/event/ngx_event_pipe.c:271
271 src/event/ngx_event_pipe.c: No such file or directory.
in src/event/ngx_event_pipe.c
(gdb) p *p->in
$11 = {buf = 0x7524d8, next = 0x7523a8}
(gdb) p *p->in->buf
$12 = {pos = 0x2b50cc908010 "½:÷ü>Gò\223ÿ", last = 0x2b50cc918008 "\001\006", file_pos = 0, file_last = 0, start = 0x2b50cc908010 "½:÷ü>Gò\223ÿ", end = 0x2b50cc948010 "", tag = 0x5c8480,
file = 0x0, shadow = 0x752528, temporary = 1, memory = 0, mmap = 0, recycled = 1, in_file = 0, flush = 0, sync = 0, last_buf = 0, last_in_chain = 0, last_shadow = 0, temp_file = 0, num = 4}
(gdb) p *p->in->next
$13 = {buf = 0x752528, next = 0x752398}
(gdb) p *p->in->next->buf
$14 = {pos = 0x2b50cc918010 "tú|=\036oøG_ý\227\027ÉïüU)ÿ", last = 0x2b50cc91be90 "", file_pos = 0, file_last = 0, start = 0x2b50cc908010 "½:÷ü>Gò\223ÿ", end = 0x2b50cc948010 "", tag = 0x5c8480,
file = 0x0, shadow = 0x752478, temporary = 1, memory = 0, mmap = 0, recycled = 1, in_file = 0, flush = 0, sync = 0, last_buf = 0, last_in_chain = 0, last_shadow = 1, temp_file = 0, num = 4}
(gdb) p *p->in->next->next
$15 = {buf = 0x7525d8, next = 0x0}
(gdb) p *p->in->next->next->buf
$16 = {
pos = 0x2b50cc949010 "gƲdäz\211»\017\027ÜÈ\026\225h^3¦\217?}\221&NG\230N\033ÏÉ.\207¼\222ñ=R\215þí\037\224|É«N\224¬\206Þ\205)J\003%dY\2348\235¥5[UnJ+¶à6&¬pÒz.K\203¼ZG©YJvõ\025óbZM«\227,\016×\236'YrKFoqhN\223\022`L\213z{Ïi,\226?\b\t)\033\217Ó\225V÷\005*÷¥W¶^>ÞU«¢$­ÿ", last = 0x2b50cc9518f0 "", file_pos = 0, file_last = 0,
start = 0x2b50cc949010 "gƲdäz\211»\017\027ÜÈ\026\225h^3¦\217?}\221&NG\230N\033ÏÉ.\207¼\222ñ=R\215þí\037\224|É«N\224¬\206Þ\205)J\003%dY\2348\235¥5[UnJ+¶à6&¬pÒz.K\203¼ZG©YJvõ\025óbZM«\227,\016×\236'YrKFoqhN\223\022`L\213z{Ïi,\226?\b\t)\033\217Ó\225V÷\005*÷¥W¶^>ÞU«¢$­ÿ", end = 0x2b50cc989010 "", tag = 0x5c8480, file = 0x0, shadow = 0x752578, temporary = 1, memory = 0, mmap = 0,
recycled = 1, in_file = 0, flush = 0, sync = 0, last_buf = 0, last_in_chain = 0, last_shadow = 1, temp_file = 0, num = 5}
(gdb) p *p->in->next->next->next
Cannot access memory at address 0x0

_______________________________________________


(gdb) p *p->free
$17 = {buf = 0x752428, next = 0x752290}
(gdb) p *p->free->buf
$18 = {
pos = 0x2b50cc843010 "¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î"...,
last = 0x2b50cc843010 "¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î"..., file_pos = 0, file_last = 0,
start = 0x2b50cc843010 "¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î½×½û¯uï~ëÝ{ߺ÷^÷î"..., end = 0x2b50cc883010 "", tag = 0x5c8480, file = 0x0, shadow = 0x0, temporary = 1, memory = 0, mmap = 0, recycled = 1, in_file = 0, flush = 0, sync = 0,
last_buf = 0, last_in_chain = 0, last_shadow = 0, temp_file = 0, num = 2}
(gdb) p *p->free->next
$19 = {buf = 0x7523d8, next = 0x6024b0}
(gdb) p *p->free->next->buf
$20 = {pos = 0x0, last = 0x0, file_pos = 0, file_last = 0, start = 0x0, end = 0x0, tag = 0x5c8480, file = 0x0, shadow = 0x0, temporary = 1, memory = 0, mmap = 0, recycled = 1, in_file = 0,
flush = 0, sync = 0, last_buf = 0, last_in_chain = 0, last_shadow = 0, temp_file = 0, num = 0}
(gdb)
$21 = {pos = 0x0, last = 0x0, file_pos = 0, file_last = 0, start = 0x0, end = 0x0, tag = 0x5c8480, file = 0x0, shadow = 0x0, temporary = 1, memory = 0, mmap = 0, recycled = 1, in_file = 0,
flush = 0, sync = 0, last_buf = 0, last_in_chain = 0, last_shadow = 0, temp_file = 0, num = 0}
(gdb) p *p->free->next->next
$22 = {buf = 0x602460, next = 0x6024c0}
(gdb) p *p->free->next->next->buf
$23 = {pos = 0x0, last = 0x0, file_pos = 0, file_last = 0, start = 0x0, end = 0x0, tag = 0x5c8480, file = 0x0, shadow = 0x0, temporary = 1, memory = 0, mmap = 0, recycled = 1, in_file = 0,
flush = 0, sync = 0, last_buf = 0, last_in_chain = 0, last_shadow = 0, temp_file = 0, num = 0}
(gdb) p *p->free->next->next->next
$24 = {buf = 0x7510f0, next = 0x0}
(gdb) p *p->free->next->next->next->buf
$25 = {pos = 0x0, last = 0x0, file_pos = 0, file_last = 0, start = 0x0, end = 0x0, tag = 0x5c8480, file = 0x0, shadow = 0x0, temporary = 1, memory = 0, mmap = 0, recycled = 1, in_file = 0,
flush = 0, sync = 0, last_buf = 0, last_in_chain = 0, last_shadow = 0, temp_file = 0, num = 0}
(gdb) p *p->free->next->next->next->next
Cannot access memory at address 0x0
(gdb) p *p->free->next->next->next->next->buf
Cannot access memory at address 0x0