linux-kernel - Re: [PATCH] kernel/perf: correct return code of rb_alloc_aux() if !has

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Message-ID: <877f06zvz8.fsf@ashishki-desk.ger.corp.intel.com>
Date:   Tue, 20 Jun 2017 15:26:03 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
        peterz@...radead.org, mingo@...hat.com, acme@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Pu Hou <bjhoupu@...ux.vnet.ibm.com>,
        Thomas-Mich Richter <tmricht@...ux.vnet.ibm.com>
Subject: Re: [PATCH] kernel/perf: correct return code of rb_alloc_aux() if !has_aux(ev)

Hendrik Brueckner <brueckner@...ux.vnet.ibm.com> writes:

> If the event for which an AUX area is about to be allocated, does
> not support setting up an AUX area, rb_alloc_aux() return -ENOTSUPP.
>
> This error condition is being returned unfiltered to the user space,
> and, for example, the perf tools fails with:
>
>   failed to mmap with 524 (INTERNAL ERROR: strerror_r(524, 0x3fff497a1c8, 512)=22)
>
> This error can be easily seen with "perf record -m 128,256 -e cpu-clock".
>
> The 524 error code maps to -ENOTSUPP (in rb_alloc_aux()). The -ENOTSUPP
> error code shall be only used within the kernel.  So the correct error
> code would then be -EOPNOTSUPP.
>
> With this commit, the perf tool then reports:
>
>   failed to mmap with 95 (Operation not supported)
>
> which is more clear.

Acked-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>

Curious as to why does the tool allow this.

Regards,
--
Alex