Re: [PATCH] btrfs/187: fix test failure when using bash 5.0+ with debug enabled

[Boris Burkov <boris@bur.io>]

On Tue, Apr 27, 2021 at 04:00:09PM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> When running btrfs/187 with a bash 5.0+ build that has debug enabled, the
> test fails due to an unexpected warning message from bash:
> 
>   $ ./check btrfs/187
>   FSTYP         -- btrfs
>   PLATFORM      -- Linux/x86_64 debian9 5.12.0-rc8-btrfs-next-92 #1 SMP PREEMPT Wed Apr 21 10:36:03 WEST 2021
>   MKFS_OPTIONS  -- /dev/sdc
>   MOUNT_OPTIONS -- /dev/sdc /home/fdmanana/btrfs-tests/scratch_1
> 
>   btrfs/187 436s ... - output mismatch (see /xfstests/results//btrfs/187.out.bad)
>       --- tests/btrfs/187.out	2020-10-16 23:13:46.550152492 +0100
>       +++ /xfstests/results//btrfs/187.out.bad	2021-04-27 14:57:02.623941700 +0100
>       @@ -1,3 +1,4 @@
>        QA output created by 187
>        Create a readonly snapshot of 'SCRATCH_MNT' in 'SCRATCH_MNT/snap1'
>        Create a readonly snapshot of 'SCRATCH_MNT' in 'SCRATCH_MNT/snap2'
>       +/xfstests/tests/btrfs/187: line 1: warning: wait_for: recursively setting old_sigint_handler to wait_sigint_handler: running_trap = 16
>       ...
>       (Run 'diff -u /xfstests/tests/btrfs/187.out /xfstests/results//btrfs/187.out.bad'  to see the entire diff)
>   Ran: btrfs/187
>   Failures: btrfs/187
>   Failed 1 of 1 tests
> 
> This is because the process running dedupe_files_loop() executes the 'wait'
> command in the trap it has setup and very often it receives the SIGTERM
> signal while it is running the 'wait' command in the while loop of that
> function - so executing the trap makes bash run 'wait' while it is already
> running 'wait', triggering the warning message from bash.
> 
> That warning message was added in bash 5.0 by commit 36f89ff1d8b761
> ("SIGINT trap handler SIGINT loop fix"):
> 
>   https://git.savannah.gnu.org/cgit/bash.git/commit/?id=36f89ff1d8b761c815d8993e9833e6357a57fc6b
> 
> So fix this by making the trap set a local variable named 'stop' to the
> value 1 and have the loop exit when the local variable 'stop' is 1.
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Reviewed-by: Boris Burkov <boris@bur.io>

> ---
>  tests/btrfs/187 | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/tests/btrfs/187 b/tests/btrfs/187
> index b2d3e4f0..7da09abd 100755
> --- a/tests/btrfs/187
> +++ b/tests/btrfs/187
> @@ -64,9 +64,19 @@ dedupe_two_files()
>  
>  dedupe_files_loop()
>  {
> -	trap "wait; exit" SIGTERM
> -
> -	while true; do
> +	local stop=0
> +
> +	# Avoid executing 'wait' inside the trap, because when we receive
> +	# SIGTERM we might be already executing the wait command in the while
> +	# loop below. When that is the case, bash 5.0+ with debug enabled prints
> +	# a warning message that makes the test fail due to a mismatch with the
> +	# golden output. That warning message is the following:
> +	#
> +	# warning: wait_for: recursively setting old_sigint_handler to wait_sigint_handler: running_trap = 16
> +	#
> +	trap "stop=1" SIGTERM
> +
> +	while [ $stop -eq 0 ]; do
>  		for ((i = 1; i <= 5; i++)); do
>  			dedupe_two_files &
>  		done
> -- 
> 2.28.0
>