Re: [PATCH perf-tools-next v10 01/10] perf ftrace: Handle signals, non-blocking reads and pager exits in __cmd_ftrace()

[sashiko-bot@kernel.org]

> In __cmd_ftrace(), trace_fd is configured for non-blocking I/O via
> fcntl(trace_fd, F_SETFL, O_NONBLOCK) and polled using poll(). However,
> the polling loop previously treated any negative return code from poll()
> or read() as an unrecoverable failure.
> 
> If poll() or read() is interrupted by a non-fatal signal (i.e. SIGWINCH
> upon terminal resizing), errno is set to EINTR. Furthermore, read() on
> trace_pipe can return EAGAIN/EWOULDBLOCK even after poll() indicates
> POLLIN (for instance, under concurrent readers, spurious wakeups, or
> block-mode trace iterator options). In all such cases, breaking from the
> loop causes perf ftrace to terminate tracing prematurely.
> 
> Additionally, output errors on stdout (i.e. when a pager or consumer
> process exits, closing the downstream pipe) were ignored by fflush(),
> leaving __cmd_ftrace() polling indefinitely until the workload
> completes.
> 
> Resolve these concerns by retrying poll() upon receiving EINTR, retrying
> read() on EAGAIN, EWOULDBLOCK, and EINTR, and breaking on EOF (n == 0).
> Furthermore, detect stdout errors and broken pipes via fflush() and
> ferror() to exit immediately when the downstream output sink closes, and
> handle EINTR and ferror(stdout) cleanly in the subsequent buffer
> draining loop.
> 
> Fixes: d01f4e8db22c ("perf ftrace: Introduce new 'ftrace' tool")
> Cc: stable@vger.kernel.org
> Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>

Sashiko has reviewed this patch and found no issues.

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