FYI, we noticed the following commit (built with gcc-7): commit: ef1317a1b9a347cdc3967a2048046e8fb4db94ba ("btrfs: do not allow reservations if we have pending tickets") https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master in testcase: aim7 with following parameters:     test: disk_rr     load: 500 on test machine: Intel(R) Xeon(R) CPU E5-2697 v2 @ 2.70GHz with 64G memory caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace): user :notice: [ 33.139372] 2019-11-04 07:12:53 echo "/fs/md0" > config user :notice: [ 33.148100] 2019-11-04 07:12:53 user :notice: [ 33.154092] ( user :notice: [ 33.158802] echo lkp-ivb-2ep1 user :notice: [ 33.165059] echo disk_rr user :notice: [ 33.172771] echo 1 user :notice: [ 33.177828] echo 500 user :notice: [ 33.182984] echo 2 user :notice: [ 33.187990] echo 500 user :notice: [ 33.193085] echo 1 user :notice: [ 33.198312] ) | ./multitask -t & user :notice: [ 33.207560] AIM Multiuser Benchmark - Suite VII v1.1, January 22, 1996 user :notice: [ 33.218340] Copyright (c) 1996 - 2001 Caldera International, Inc. user :notice: [ 33.227911] All Rights Reserved. user :notice: [ 33.240271] Machine's name : Machine's configuration : Number of iterations to run [1 to 10] : user :notice: [ 33.263230] Information for iteration #1 user :notice: [ 33.271789] Starting number of operation loads [1 to 10000] : 1) Run to crossover user :notice: [ 33.288044] 2) Run to specific operation load Enter [1 or 2]: Maximum number of operation loads to simulate [500 to 10000]: Operation load increment [1 to 100] : user :notice: [ 33.310911] Using disk directory user :notice: [ 33.318091] HZ is <100> user :notice: [ 33.324287] AIM Multiuser Benchmark - Suite VII Run Beginning user :notice: [ 33.336401] Tasks jobs/min jti jobs/min/task real cpu kern :info : [ 46.969180] perf: interrupt took too long (2513 > 2500), lowering kernel.perf_event_max_sample_rate to 79000 kern :info : [ 46.980877] perf: interrupt took too long (3153 > 3141), lowering kernel.perf_event_max_sample_rate to 63000 kern :info : [ 46.992352] perf: interrupt took too long (3947 > 3941), lowering kernel.perf_event_max_sample_rate to 50000 kern :info : [ 47.100977] perf: interrupt took too long (4935 > 4933), lowering kernel.perf_event_max_sample_rate to 40000 kern :info : [ 47.203012] perf: interrupt took too long (6238 > 6168), lowering kernel.perf_event_max_sample_rate to 32000 kern :info : [ 47.689325] perf: interrupt took too long (7811 > 7797), lowering kernel.perf_event_max_sample_rate to 25000 kern :info : [ 48.280299] perf: interrupt took too long (9863 > 9763), lowering kernel.perf_event_max_sample_rate to 20000 kern :info : [ 49.579335] perf: interrupt took too long (12358 > 12328), lowering kernel.perf_event_max_sample_rate to 16000 kern :warn : [ 51.987379] WARNING: stack recursion on stack type 4 kern :warn : [ 51.987388] WARNING: can't dereference registers at 0000000095915d40 for ip swapgs_restore_regs_and_return_to_usermode+0x79/0x87 kern :notice: [ 76.160511] random: crng init done kern :notice: [ 76.164952] random: 7 urandom warning(s) missed due to ratelimiting user :err : [ 2230.687280] disk_rr(): No space left on device user :err : [ 2231.786740] disk_rr : cannot write /fs/md0/tmpb.0243400022 user :err : [ 2231.796023] disk_rr(): No space left on device user :err : [ 2231.804660] disk_rr : cannot write /fs/md0/tmpb.0220800023 user :err : [ 2231.814027] disk_rr(): No space left on device user :err : [ 2231.822652] disk_rr : cannot write /fs/md0/tmpb.0238900023 user :err : [ 2231.831991] disk_rr(): No space left on device Thanks, Rong Chen