Re: [PATCH] blktrace: use debug print to report dropped events

[Damien Le Moal <dlemoal@kernel.org>]

On 10/28/25 11:46 AM, Chaitanya Kulkarni wrote:
> The WARN_ON_ONCE introduced in
> commit f9ee38bbf70f ("blktrace: add block trace commands for zone operations") 
> triggers kernel warnings when zone operations are traced with blktrace
> version 1. This can spam the kernel log during normal operation with
> zoned block devices when userspace is using the legacy blktrace
> protocol.
> 
> Currently blktrace implementation drops newly added REQ_OP_ZONE_XXX
> when blktrace userspce version is set to 1.
> 
> Remove the WARN_ON_ONCE and quietly filter these events. Add a
> rate-limited debug message to help diagnose potential issues without
> flooding the kernel log. The debug message can be enabled via dynamic
> debug when needed for troubleshooting.
> 
> This approach is more appropriate as encountering zone operations with
> blktrace v1 is an expected condition that should be handled gracefully
> rather than warned about, since users may be running older blktrace
> userspace tools that only support version 1 of the protocol.
> 
> With this patch :-
> linux-block (for-next) # git log -1 
> commit c8966006a0971d2b4bf94c0426eb7e4407c6853f (HEAD -> for-next)
> Author: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
> Date:   Mon Oct 27 19:26:53 2025 -0700
> 
>     blktrace: use debug print to report dropped events
> linux-block (for-next) # cdblktests
> blktests (master) # ./check blktrace
> blktrace/001 (blktrace zone management command tracing)      [passed]
>     runtime  3.805s  ...  3.889s
> blktests (master) # dmesg  -c
> blktests (master) #  echo "file kernel/trace/blktrace.c +p" > /sys/kernel/debug/dynamic_debug/control
> blktests (master) # ./check blktrace
> blktrace/001 (blktrace zone management command tracing)      [passed]
>     runtime  3.889s  ...  3.881s
> blktests (master) # dmesg  -c
> [   77.826237] blktrace: blktrace v1 cannot trace zone operation 0x1000190001
> [   77.826260] blktrace: blktrace v1 cannot trace zone operation 0x1000190004
> [   77.826282] blktrace: blktrace v1 cannot trace zone operation 0x1001490007
> [   77.826288] blktrace: blktrace v1 cannot trace zone operation 0x1001890008
> [   77.826343] blktrace: blktrace v1 cannot trace zone operation 0x1000190001
> [   77.826347] blktrace: blktrace v1 cannot trace zone operation 0x1000190004
> [   77.826350] blktrace: blktrace v1 cannot trace zone operation 0x1001490007
> [   77.826354] blktrace: blktrace v1 cannot trace zone operation 0x1001890008
> [   77.826373] blktrace: blktrace v1 cannot trace zone operation 0x1000190001
> [   77.826377] blktrace: blktrace v1 cannot trace zone operation 0x1000190004
> blktests (master) #  echo "file kernel/trace/blktrace.c -p" > /sys/kernel/debug/dynamic_debug/control
> blktests (master) # ./check blktrace
> blktrace/001 (blktrace zone management command tracing)      [passed]
>     runtime  3.881s  ...  3.824s
> blktests (master) # dmesg  -c 
> blktests (master) # 
> 
> Reported-by: syzbot+153e64c0aa875d7e4c37@syzkaller.appspotmail.com
> Fixes: f9ee38bbf70f ("blktrace: add block trace commands for zone operations")
> Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>

Looks good.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

-- 
Damien Le Moal
Western Digital Research