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Message-ID: <ZcT5540Bv7U8qoUa@casper.infradead.org>
Date: Thu, 8 Feb 2024 15:57:27 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Dave Chinner <david@...morbit.com>
Cc: Miklos Szeredi <miklos@...redi.hu>,
lsf-pc <lsf-pc@...ts.linux-foundation.org>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [LSF/MM/BPF TOPIC] tracing the source of errors
On Thu, Feb 08, 2024 at 08:37:29AM +1100, Dave Chinner wrote:
> ftrace using the function_graph tracer will emit the return values
> of the functions if you use it with the 'funcgraph-retval' option.
OK, but that may not be fine grained enough. Why is mmap() returning
-ENOMEM?
unsigned long do_mmap(struct file *file, unsigned long addr,
..
/* Careful about overflows.. */
len = PAGE_ALIGN(len);
if (!len)
return -ENOMEM;
..
/* Too many mappings? */
if (mm->map_count > sysctl_max_map_count)
return -ENOMEM;
So it can distinguish between mmap() returning ENOMEM because
get_unmapped_area() returned ENOMEM and do_mmap() returning ENOMEM of
its own accord (right?), but it can't tell you which of the above two
cases you hit. Or can it?
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