From: Kent Overstreet <kent.overstreet@gmail.com>
To: Josef Bacik <josef@toxicpanda.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Dave Chinner <dchinner@redhat.com>,
darrick.wong@oracle.com, tytso@mit.edu,
linux-btrfs@vger.kernel.org, clm@fb.com, jbacik@fb.com,
viro@zeniv.linux.org.uk, willy@infradead.org,
peterz@infradead.org
Subject: Re: [PATCH 00/10] RFC: assorted bcachefs patches
Date: Fri, 18 May 2018 14:28:49 -0400 [thread overview]
Message-ID: <20180518182849.GF31737@kmo-pixel> (raw)
In-Reply-To: <20180518180324.ymwbajfw5wsfrlth@destiny>
On Fri, May 18, 2018 at 02:03:25PM -0400, Josef Bacik wrote:
> There's nothing stopping us from doing that, it just uses a kprobe to override
> the function with our helper, so we could conceivably put it anywhere in the
> function. The reason I limited it to individual functions was because it was
> easier than trying to figure out the side-effects of stopping mid-function. If
> I needed to fail mid-function I just added a helper where I needed it and failed
> that instead. I imagine safety is going to be of larger concern if we allow bpf
> scripts to randomly return anywhere inside a function, even if the function is
> marked as allowing error injection. Thanks,
Ahh no, that's not what I want... here's an example:
https://evilpiepirate.org/git/bcachefs.git/tree/fs/bcachefs/btree_cache.c#n674
Here we've got to do this thing which can race - which is fine, we just need to
check for and handle the race, on line 709 - but actually exercising that with a
test is difficult since it requires a heavily multithreaded workload with btree
nodes getting evicted to see it happen, so - it pretends the race happened if
race_fault() returns true. The race_fault() invocation shows up in debugfs,
where userspace can tell it to fire.
the way it works is dynamic_fault() is a macro that expands to a static struct
dfault_descriptor, stuck in a particular linker section so the dynamic fault
code can find them and stick them in debugfs (which is also the way dynamic
debug works).
#define dynamic_fault(_class) \
({ \
static struct _dfault descriptor \
__used __aligned(8) __attribute__((section("__faults"))) = { \
.modname = KBUILD_MODNAME, \
.function = __func__, \
.filename = __FILE__, \
.line = __LINE__, \
.class = _class, \
}; \
\
static_key_false(&descriptor.enabled) && \
__dynamic_fault_enabled(&descriptor); \
})
Honestly it still seems like the cleanest and safest way of doing it to me...
prev parent reply other threads:[~2018-05-18 18:28 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-18 7:48 [PATCH 00/10] RFC: assorted bcachefs patches Kent Overstreet
2018-05-18 7:49 ` [PATCH 01/10] mm: pagecache add lock Kent Overstreet
2018-05-18 13:13 ` Matthew Wilcox
2018-05-18 15:53 ` Christoph Hellwig
2018-05-18 17:45 ` Kent Overstreet
2018-05-23 23:55 ` Notes on locking for pagacache consistency (was: [PATCH 01/10] mm: pagecache add lock) Kent Overstreet
2018-05-20 22:45 ` [PATCH 01/10] mm: pagecache add lock Kent Overstreet
2018-05-23 15:22 ` Christoph Hellwig
2018-05-23 17:12 ` Kent Overstreet
2018-05-18 7:49 ` [PATCH 02/10] mm: export find_get_pages() Kent Overstreet
2018-05-18 16:00 ` Christoph Hellwig
2018-05-18 7:49 ` [PATCH 03/10] locking: bring back lglocks Kent Overstreet
2018-05-18 9:51 ` Peter Zijlstra
2018-05-18 10:13 ` Kent Overstreet
2018-05-18 11:03 ` Peter Zijlstra
2018-05-18 11:39 ` Kent Overstreet
2018-05-18 7:49 ` [PATCH 04/10] locking: export osq_lock()/osq_unlock() Kent Overstreet
2018-05-18 9:52 ` Peter Zijlstra
2018-05-18 10:18 ` Kent Overstreet
2018-05-18 11:08 ` Peter Zijlstra
2018-05-18 11:32 ` Kent Overstreet
2018-05-18 11:40 ` Peter Zijlstra
2018-05-18 12:40 ` Kent Overstreet
2018-05-18 7:49 ` [PATCH 05/10] don't use spin_lock_irqsave() unnecessarily Kent Overstreet
2018-05-18 16:01 ` Christoph Hellwig
2018-05-18 7:49 ` [PATCH 06/10] Generic radix trees Kent Overstreet
2018-05-18 16:02 ` Christoph Hellwig
2018-05-18 17:38 ` Kent Overstreet
2018-05-18 7:49 ` [PATCH 07/10] bcache: optimize continue_at_nobarrier() Kent Overstreet
2018-05-18 7:49 ` [PATCH 08/10] bcache: move closures to lib/ Kent Overstreet
2018-05-18 16:02 ` Christoph Hellwig
2018-05-18 7:49 ` [PATCH 09/10] closures: closure_wait_event() Kent Overstreet
2018-05-18 7:49 ` [PATCH 10/10] Dynamic fault injection Kent Overstreet
2018-05-18 16:02 ` Christoph Hellwig
2018-05-18 17:37 ` Kent Overstreet
2018-05-18 19:05 ` Andreas Dilger
2018-05-18 19:10 ` Kent Overstreet
2018-05-18 20:54 ` Andreas Dilger
2018-05-18 7:55 ` [PATCH 00/10] RFC: assorted bcachefs patches Kent Overstreet
2018-05-18 17:45 ` Josef Bacik
2018-05-18 17:49 ` Kent Overstreet
2018-05-18 18:03 ` Josef Bacik
2018-05-18 18:28 ` Kent Overstreet [this message]
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