There is a subtle bug that if the atomic flag changes
between the time it was checked and the second time
it was checked, sleep.c would potentially block a
process that had specified O_NONBLOCK. This fixes
the bug by using atomic_cmpxchg instead of atomic_read.
For x86 architecture, the system call table cannot be used to invoke
a system call after commit 1e3ad78 since v6.9. This commit has been
backported to long term stable kernels, like v5.15.154+, v6.1.85+,
v6.6.26+ and v6.8.5+[1]. In this case, thanks to Kprobes, a hook can be
used instead on the system call entry to intercept the system call.
[1] https://stackoverflow.com/a/78607015
Co-authored-by: Hao Dong <hao.dong.work@outlook.com>
When raw_copy_to_user() failed in vinput_read(), the function would set
'count' to -EFAULT and then subtract EFAULT from '*offset'. However,
modifying '*offset' on raw_copy_to_user() failure was incorrect. Fix
this behavior by changing count = -EFAULT to return -EFAULT.
When kzalloc fails to allocate memory and returns NULL, it leads to a
NULL pointer dereference error later on. Add a check for the return
value of kzalloc. When kzalloc fails to allocate memory, it prints an
error message and returns ERR_PTR(-ENOMEM).
The last parameter of request_threaded_irq must be a globally unique
cookie[1]. Usually this would be the device struct received by probe().
Since we are not using driver model, pass the gpio structs instead.
[1] https://docs.kernel.org/core-api/genericirq.html
The past content in the crypto section lacks informative descriptions,
and there should be a proper procedure to demonstrate how Linux
cryptography works. Due to poor maintenance, let's drop the section.
The code 'case -EINPROGRESS || -EBUSY: ' is the same as
'case -115 || -16 :' at compiler time, as both error code are
implemented with macro like '#define EBUSY 16'.
The code above is essentially the same as 'case 1:'. In C, there is no
real boolean value. Boolean-like value will be converted to 1 or 0.
It does not matter too much if the '-EINPROGRESS || -EBUSY' is
calculated at build time or at runtime. In both case, it will compare
the 'rc' with 1 in the switch expression. It will not compare the
'rc' with any real error code number. When the code is really '-EBUSY',
the execution will fallback to the default branch.
And in practice, most of the compilers will do this simple compile-time
static calculation, and generate code like
static int test_skcipher_result(struct skcipher_def *sk, int rc)
{
switch (rc) {
case 0:
break;
case 1:
rc = wait_for_completion_interruptible(&sk->result.completion);
/* code removed for conciseness */
break;
default:
pr_info("skcipher encrypt returned with %d result %d\n", rc,
sk->result.err);
break;
}
init_completion(&sk->result.completion);
return rc;
}
sys_call_table is already declared in arch/x86/include/asm/syscall.h but of
cource not exported by the kernel.
before this commit, gcc complains as follows:
/usr/src/linux-headers-6.1.0-16-common/arch/x86/include/asm/syscall.h:21:29:
note: previous declaration of 'sys_call_table' with type 'long int (*
const[])(const struct pt_regs *)'
21 | extern const sys_call_ptr_t sys_call_table[];
In Debian, the name syscall conflicts with this patch:
in debian kernel source tree:
debian/patches/features/x86/x86-make-x32-syscall-support-conditional.patch
mailing list url:
https://lore.kernel.org/lkml/1415245982.3398.53.camel@decadent.org.uk/T/#u
which introduces a parameter named syscall.x32. So change our name.
schedule_work adds work to global workqueue. In this example, we create a local workqueue. Use the local workqueue by calling queue_work(), instead of putting work on the global workqueue.
dmesg only flushes when it encounter a newline. Without a newline, the line
is held in memory pending another printk. In this particular example
(example_atomic.c), the last pr_info in atomic_bitwise() prints when
another printk happens (either by another module, or __exit for this
module.
This can be confusing to new learner. This patch adds a newline to the last
pr_info forcing dmesg to print to the screen when the module is loaded.
Two struct completion(s) are encapsulated within another 'struct machine'.
Simplify the code by removing the outer struct and let the struct
completion(s) be self-standing.
Update description in tex to match code.
From v6.4, class_create() does not have module *
See commit 11ba11 :
> driver core: class: remove module * from class_create()
>
> The module pointer in class_create() never actually did anything,
> and it shouldn't have been requred to be set as a parameter even
> if it did something. So just remove it and fix up all callers of the
> function in the kernel tree at the same time.
This patch introduces static key technique and adds a kernel module
to demostrate how to use static key to optimize an almost unlikely
branch, the module can interact with userspace thru a character device.
Signed-off-by: Peter Lin <peterlin@qilai.dev>
Since v5.17-rc1, particularly after the commit cead1855266 ("exit:
Rename complete_and_exit to kthread_complete_and_exit"),
complete_and_exit() is renamed to kthread_complete_and_exit().
Close#188
The rule of thumb is to include the headers we are the direct user of.
In particular, if we need an atomic API, we include <linux/atomic.h>.
On the other hand we should not use headers for no reason. In particular,
if we are not doing any IRQ job, why is the <linux/irq.h> included?
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
platform_driver_register() macro already does the correct assignment for
the owner of the driver.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Since sys_open is deprecated and some architectures don't support it.
We switch the implementation to sys_openat.
Moreover, in some architectures like x86-64, the prototype of syscall,
for example, openat(), might have been changed to struct pt_regs [1]
but we cannot promise that so support the two types
(sys_openat and pt_regs).
Also, to prevent other untraced tasks print out the information, add
the uid checking in our_sys_openat().
[1] https://lore.kernel.org/lkml/20180405095307.3730-1-linux@dominikbrodowski.net/Close#159
It failed silently when crypto_alloc_tfm() failed, so add an error
message to inform the developer to enable sha256 algorithm support.
Signed-off-by: Yu Chien Peter Lin <peterlin.tw@pm.me>
To make sure the behavior of the read and write operations are correct
with offset, update it each time. Also, since it is using the offset,
modify the part of read for removing unnecessary variable.
Since The length of the message buffer is BUF_LEN. When writing the
BUF_LEN length of the string it will overwrite the last character
(usually it is '\0' from the initialization). And, because the read
operation uses the character in the message buffer ('\0') to stop the
read loop. It will cause the read operation will read out of the
message buffer when the length parameter of read() is not lower than
or equal to BUF_LEN. So add one more byte space to avoid this problem.
