Revision 59771079c18c44e39106f0f30054025acafadb41 authored by Linus Torvalds on 19 December 2012, 15:18:35 UTC, committed by Linus Torvalds on 19 December 2012, 15:18:35 UTC
Commit 8dd2cb7e880d ("block: discard granularity might not be power of 2") changed a couple of 'binary and' operations into modulus operations. Which turned the harmless case of a zero discard_granularity into a possible divide-by-zero. The code also had a much more subtle bug: it was doing the modulus of a value in bytes using 'sector_t'. That was always conceptually wrong, but didn't actually matter back when the code assumed a power-of-two granularity: we only looked at the low bits anyway. But with potentially arbitrary sector numbers, using a 'sector_t' to express bytes is very very wrong: depending on configuration it limits the starting offset of the device to just 32 bits, and any overflow would result in a wrong value if the modulus wasn't a power-of-two. So re-write the code to not only protect against the divide-by-zero, but to do the starting sector arithmetic in sectors, and using the proper types. [ For any mathematicians out there: it also looks monumentally stupid to do the 'modulo granularity' operation *twice*, never mind having a "+ granularity" in the second modulus op. But that's the easiest way to avoid negative values or overflow, and it is how the original code was done. ] Reported-by: Ingo Molnar <mingo@kernel.org> Reported-by: Doug Anderson <dianders@chromium.org> Cc: Neil Brown <neilb@suse.de> Cc: Shaohua Li <shli@fusionio.com> Acked-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent 752451f
sparse.txt
Copyright 2004 Linus Torvalds
Copyright 2004 Pavel Machek <pavel@ucw.cz>
Copyright 2006 Bob Copeland <me@bobcopeland.com>
Using sparse for typechecking
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"__bitwise" is a type attribute, so you have to do something like this:
typedef int __bitwise pm_request_t;
enum pm_request {
PM_SUSPEND = (__force pm_request_t) 1,
PM_RESUME = (__force pm_request_t) 2
};
which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is
there because sparse will complain about casting to/from a bitwise type,
but in this case we really _do_ want to force the conversion). And because
the enum values are all the same type, now "enum pm_request" will be that
type too.
And with gcc, all the __bitwise/__force stuff goes away, and it all ends
up looking just like integers to gcc.
Quite frankly, you don't need the enum there. The above all really just
boils down to one special "int __bitwise" type.
So the simpler way is to just do
typedef int __bitwise pm_request_t;
#define PM_SUSPEND ((__force pm_request_t) 1)
#define PM_RESUME ((__force pm_request_t) 2)
and you now have all the infrastructure needed for strict typechecking.
One small note: the constant integer "0" is special. You can use a
constant zero as a bitwise integer type without sparse ever complaining.
This is because "bitwise" (as the name implies) was designed for making
sure that bitwise types don't get mixed up (little-endian vs big-endian
vs cpu-endian vs whatever), and there the constant "0" really _is_
special.
__bitwise__ - to be used for relatively compact stuff (gfp_t, etc.) that
is mostly warning-free and is supposed to stay that way. Warnings will
be generated without __CHECK_ENDIAN__.
__bitwise - noisy stuff; in particular, __le*/__be* are that. We really
don't want to drown in noise unless we'd explicitly asked for it.
Using sparse for lock checking
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The following macros are undefined for gcc and defined during a sparse
run to use the "context" tracking feature of sparse, applied to
locking. These annotations tell sparse when a lock is held, with
regard to the annotated function's entry and exit.
__must_hold - The specified lock is held on function entry and exit.
__acquires - The specified lock is held on function exit, but not entry.
__releases - The specified lock is held on function entry, but not exit.
If the function enters and exits without the lock held, acquiring and
releasing the lock inside the function in a balanced way, no
annotation is needed. The tree annotations above are for cases where
sparse would otherwise report a context imbalance.
Getting sparse
~~~~~~~~~~~~~~
You can get latest released versions from the Sparse homepage at
https://sparse.wiki.kernel.org/index.php/Main_Page
Alternatively, you can get snapshots of the latest development version
of sparse using git to clone..
git://git.kernel.org/pub/scm/devel/sparse/sparse.git
DaveJ has hourly generated tarballs of the git tree available at..
http://www.codemonkey.org.uk/projects/git-snapshots/sparse/
Once you have it, just do
make
make install
as a regular user, and it will install sparse in your ~/bin directory.
Using sparse
~~~~~~~~~~~~
Do a kernel make with "make C=1" to run sparse on all the C files that get
recompiled, or use "make C=2" to run sparse on the files whether they need to
be recompiled or not. The latter is a fast way to check the whole tree if you
have already built it.
The optional make variable CF can be used to pass arguments to sparse. The
build system passes -Wbitwise to sparse automatically. To perform endianness
checks, you may define __CHECK_ENDIAN__:
make C=2 CF="-D__CHECK_ENDIAN__"
These checks are disabled by default as they generate a host of warnings.
![swh spinner](/static/img/swh-spinner.gif)
Computing file changes ...