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selftests/ftrace: Fix trace_marker_raw test on 64K page kernels

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On ARM64 kernels with 64K pages, the trace_marker_raw test fails because
bash's printf builtin uses stdio buffering which splits output into
multiple small write() calls to the tracefs file. Since each individual
write is within TRACE_MARKER_MAX_SIZE (4096), they all succeed, causing
the "too big" write test to incorrectly pass.

Fix by writing through dd with iflag=fullblock to guarantee a single
atomic write() syscall to trace_marker_raw.

Link: https://lore.kernel.org/r/20260601023251.1916483-1-dtcccc@linux.alibaba.com
Fixes: 37f4660138 ("selftests/tracing: Add basic test for trace_marker_raw file")
Signed-off-by: Tianchen Ding <dtcccc@linux.alibaba.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
This commit is contained in:
Tianchen Ding 2026-06-01 10:32:51 +08:00 committed by Shuah Khan
parent 808c447df2
commit 65f26d15f7
1 changed files with 11 additions and 3 deletions
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14
tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
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@ -36,15 +36,23 @@ make_str() {
data=`printf -- 'X%.0s' $(seq $cnt)`
printf "${val}${data}"
# Return escape-sequence text (e.g. "\003\000..."); the caller
# converts to binary. Shell command substitution strips NUL bytes,
# so the binary form cannot survive being captured into a variable.
printf '%s' "${val}${data}"
}
write_buffer() {
id=$1
size=$2
# write the string into the raw marker
make_str $id $size > trace_marker_raw
str=`make_str $id $size`
len=`printf "$str" | wc -c`
# Pipe through dd to ensure a single atomic write() syscall
# on architectures with 64K pages, where shell's printf builtin
# uses stdio buffering which may split the output into multiple
# writes.
printf "$str" | dd of=trace_marker_raw bs=$len iflag=fullblock
}