mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-06 18:36:40 +07:00
14ebc28e07
- Move errseq.rst into core-api - Add errseq to the core-api index - Promote the header to a more prominent header type, otherwise we get three entries in the table of contents. - Reformat the table to look nicer and be a little more proportional in terms of horizontal width per bit (the SF bit is still disproportionately large, but there's no way to fix that). - Include errseq kernel-doc in the errseq.rst - Neaten some kernel-doc markup Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com> Reviewed-by: Jeff Layton <jlayton@redhat.com> Reviewed-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
212 lines
6.6 KiB
C
212 lines
6.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
#include <linux/err.h>
|
|
#include <linux/bug.h>
|
|
#include <linux/atomic.h>
|
|
#include <linux/errseq.h>
|
|
|
|
/*
|
|
* An errseq_t is a way of recording errors in one place, and allowing any
|
|
* number of "subscribers" to tell whether it has changed since a previous
|
|
* point where it was sampled.
|
|
*
|
|
* It's implemented as an unsigned 32-bit value. The low order bits are
|
|
* designated to hold an error code (between 0 and -MAX_ERRNO). The upper bits
|
|
* are used as a counter. This is done with atomics instead of locking so that
|
|
* these functions can be called from any context.
|
|
*
|
|
* The general idea is for consumers to sample an errseq_t value. That value
|
|
* can later be used to tell whether any new errors have occurred since that
|
|
* sampling was done.
|
|
*
|
|
* Note that there is a risk of collisions if new errors are being recorded
|
|
* frequently, since we have so few bits to use as a counter.
|
|
*
|
|
* To mitigate this, one bit is used as a flag to tell whether the value has
|
|
* been sampled since a new value was recorded. That allows us to avoid bumping
|
|
* the counter if no one has sampled it since the last time an error was
|
|
* recorded.
|
|
*
|
|
* A new errseq_t should always be zeroed out. A errseq_t value of all zeroes
|
|
* is the special (but common) case where there has never been an error. An all
|
|
* zero value thus serves as the "epoch" if one wishes to know whether there
|
|
* has ever been an error set since it was first initialized.
|
|
*/
|
|
|
|
/* The low bits are designated for error code (max of MAX_ERRNO) */
|
|
#define ERRSEQ_SHIFT ilog2(MAX_ERRNO + 1)
|
|
|
|
/* This bit is used as a flag to indicate whether the value has been seen */
|
|
#define ERRSEQ_SEEN (1 << ERRSEQ_SHIFT)
|
|
|
|
/* The lowest bit of the counter */
|
|
#define ERRSEQ_CTR_INC (1 << (ERRSEQ_SHIFT + 1))
|
|
|
|
/**
|
|
* errseq_set - set a errseq_t for later reporting
|
|
* @eseq: errseq_t field that should be set
|
|
* @err: error to set (must be between -1 and -MAX_ERRNO)
|
|
*
|
|
* This function sets the error in @eseq, and increments the sequence counter
|
|
* if the last sequence was sampled at some point in the past.
|
|
*
|
|
* Any error set will always overwrite an existing error.
|
|
*
|
|
* Return: The previous value, primarily for debugging purposes. The
|
|
* return value should not be used as a previously sampled value in later
|
|
* calls as it will not have the SEEN flag set.
|
|
*/
|
|
errseq_t errseq_set(errseq_t *eseq, int err)
|
|
{
|
|
errseq_t cur, old;
|
|
|
|
/* MAX_ERRNO must be able to serve as a mask */
|
|
BUILD_BUG_ON_NOT_POWER_OF_2(MAX_ERRNO + 1);
|
|
|
|
/*
|
|
* Ensure the error code actually fits where we want it to go. If it
|
|
* doesn't then just throw a warning and don't record anything. We
|
|
* also don't accept zero here as that would effectively clear a
|
|
* previous error.
|
|
*/
|
|
old = READ_ONCE(*eseq);
|
|
|
|
if (WARN(unlikely(err == 0 || (unsigned int)-err > MAX_ERRNO),
|
|
"err = %d\n", err))
|
|
return old;
|
|
|
|
for (;;) {
|
|
errseq_t new;
|
|
|
|
/* Clear out error bits and set new error */
|
|
new = (old & ~(MAX_ERRNO|ERRSEQ_SEEN)) | -err;
|
|
|
|
/* Only increment if someone has looked at it */
|
|
if (old & ERRSEQ_SEEN)
|
|
new += ERRSEQ_CTR_INC;
|
|
|
|
/* If there would be no change, then call it done */
|
|
if (new == old) {
|
|
cur = new;
|
|
break;
|
|
}
|
|
|
|
/* Try to swap the new value into place */
|
|
cur = cmpxchg(eseq, old, new);
|
|
|
|
/*
|
|
* Call it success if we did the swap or someone else beat us
|
|
* to it for the same value.
|
|
*/
|
|
if (likely(cur == old || cur == new))
|
|
break;
|
|
|
|
/* Raced with an update, try again */
|
|
old = cur;
|
|
}
|
|
return cur;
|
|
}
|
|
EXPORT_SYMBOL(errseq_set);
|
|
|
|
/**
|
|
* errseq_sample() - Grab current errseq_t value.
|
|
* @eseq: Pointer to errseq_t to be sampled.
|
|
*
|
|
* This function allows callers to sample an errseq_t value, marking it as
|
|
* "seen" if required.
|
|
*
|
|
* Return: The current errseq value.
|
|
*/
|
|
errseq_t errseq_sample(errseq_t *eseq)
|
|
{
|
|
errseq_t old = READ_ONCE(*eseq);
|
|
errseq_t new = old;
|
|
|
|
/*
|
|
* For the common case of no errors ever having been set, we can skip
|
|
* marking the SEEN bit. Once an error has been set, the value will
|
|
* never go back to zero.
|
|
*/
|
|
if (old != 0) {
|
|
new |= ERRSEQ_SEEN;
|
|
if (old != new)
|
|
cmpxchg(eseq, old, new);
|
|
}
|
|
return new;
|
|
}
|
|
EXPORT_SYMBOL(errseq_sample);
|
|
|
|
/**
|
|
* errseq_check() - Has an error occurred since a particular sample point?
|
|
* @eseq: Pointer to errseq_t value to be checked.
|
|
* @since: Previously-sampled errseq_t from which to check.
|
|
*
|
|
* Grab the value that eseq points to, and see if it has changed @since
|
|
* the given value was sampled. The @since value is not advanced, so there
|
|
* is no need to mark the value as seen.
|
|
*
|
|
* Return: The latest error set in the errseq_t or 0 if it hasn't changed.
|
|
*/
|
|
int errseq_check(errseq_t *eseq, errseq_t since)
|
|
{
|
|
errseq_t cur = READ_ONCE(*eseq);
|
|
|
|
if (likely(cur == since))
|
|
return 0;
|
|
return -(cur & MAX_ERRNO);
|
|
}
|
|
EXPORT_SYMBOL(errseq_check);
|
|
|
|
/**
|
|
* errseq_check_and_advance() - Check an errseq_t and advance to current value.
|
|
* @eseq: Pointer to value being checked and reported.
|
|
* @since: Pointer to previously-sampled errseq_t to check against and advance.
|
|
*
|
|
* Grab the eseq value, and see whether it matches the value that @since
|
|
* points to. If it does, then just return 0.
|
|
*
|
|
* If it doesn't, then the value has changed. Set the "seen" flag, and try to
|
|
* swap it into place as the new eseq value. Then, set that value as the new
|
|
* "since" value, and return whatever the error portion is set to.
|
|
*
|
|
* Note that no locking is provided here for concurrent updates to the "since"
|
|
* value. The caller must provide that if necessary. Because of this, callers
|
|
* may want to do a lockless errseq_check before taking the lock and calling
|
|
* this.
|
|
*
|
|
* Return: Negative errno if one has been stored, or 0 if no new error has
|
|
* occurred.
|
|
*/
|
|
int errseq_check_and_advance(errseq_t *eseq, errseq_t *since)
|
|
{
|
|
int err = 0;
|
|
errseq_t old, new;
|
|
|
|
/*
|
|
* Most callers will want to use the inline wrapper to check this,
|
|
* so that the common case of no error is handled without needing
|
|
* to take the lock that protects the "since" value.
|
|
*/
|
|
old = READ_ONCE(*eseq);
|
|
if (old != *since) {
|
|
/*
|
|
* Set the flag and try to swap it into place if it has
|
|
* changed.
|
|
*
|
|
* We don't care about the outcome of the swap here. If the
|
|
* swap doesn't occur, then it has either been updated by a
|
|
* writer who is altering the value in some way (updating
|
|
* counter or resetting the error), or another reader who is
|
|
* just setting the "seen" flag. Either outcome is OK, and we
|
|
* can advance "since" and return an error based on what we
|
|
* have.
|
|
*/
|
|
new = old | ERRSEQ_SEEN;
|
|
if (new != old)
|
|
cmpxchg(eseq, old, new);
|
|
*since = new;
|
|
err = -(new & MAX_ERRNO);
|
|
}
|
|
return err;
|
|
}
|
|
EXPORT_SYMBOL(errseq_check_and_advance);
|