Re: dd hangs when reading large partitions

[Marc Gonzalez <marc.w.gonzalez@free.fr>]

+ linux-mm

Summarizing the issue for linux-mm readers:

If I read data from a storage device larger than my system's RAM, the system freezes
once dd has read more data than available RAM.

# dd if=/dev/sde of=/dev/null bs=1M & while true; do echo m > /proc/sysrq-trigger; echo; echo; sleep 1; done
https://pastebin.ubuntu.com/p/HXzdqDZH4W/

A few seconds before the system hangs, Mem-Info shows:

[   90.986784] Node 0 active_anon:7060kB inactive_anon:13644kB active_file:0kB inactive_file:3797500kB [...]

=> 3797500kB is basically all of RAM.

I tried to locate where "inactive_file" was being increased from, and saw two signatures:

[  255.606019] __mod_node_page_state | __pagevec_lru_add_fn | pagevec_lru_move_fn | __lru_cache_add | lru_cache_add | add_to_page_cache_lru | mpage_readpages | blkdev_readpages | read_pages | __do_page_cache_readahead | ondemand_readahead | page_cache_sync_readahead

[  255.637238] __mod_node_page_state | __pagevec_lru_add_fn | pagevec_lru_move_fn | __lru_cache_add | lru_cache_add | lru_cache_add_active_or_unevictable | __handle_mm_fault | handle_mm_fault | do_page_fault | do_translation_fault | do_mem_abort | el1_da

Are these expected?

NB: the system does not hang if I specify 'iflag=direct' to dd.

According to the RCU watchdog:

[  108.466240] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[  108.466420] rcu:     1-...0: (130 ticks this GP) idle=79e/1/0x4000000000000000 softirq=2393/2523 fqs=2626 
[  108.471436] rcu:     (detected by 4, t=5252 jiffies, g=133, q=85)
[  108.480605] Task dump for CPU 1:
[  108.486483] kworker/1:1H    R  running task        0   680      2 0x0000002a
[  108.489977] Workqueue: kblockd blk_mq_run_work_fn
[  108.496908] Call trace:
[  108.501513]  __switch_to+0x174/0x1e0
[  108.503757]  blk_mq_run_work_fn+0x28/0x40
[  108.507589]  process_one_work+0x208/0x480
[  108.511486]  worker_thread+0x48/0x460
[  108.515480]  kthread+0x124/0x130
[  108.519123]  ret_from_fork+0x10/0x1c

Can anyone shed some light on what's going on?

Regards.