Revision f78d76e72a4671ea52d12752d92077788b4f5d50 authored by Linus Torvalds on 12 March 2021, 01:38:49 UTC, committed by Linus Torvalds on 12 March 2021, 01:38:49 UTC
Pull drm fixes from Dave Airlie: "Regular fixes for rc3. The i915 pull was based on the rc1 tag so I just cherry-picked the single fix from there to avoid it. The misc and amd trees seem to be on okay bases. It's a bunch of fixes across the tree, amdgpu has most of them a few ttm fixes around qxl, and nouveau. core: - Clear holes when converting compat ioctl's between 32-bits and 64-bits. docs: - Use gitlab for drm bugzilla now. ttm: - Fix ttm page pool accounting. fbdev: - Fix oops in drm_fbdev_cleanup() shmem: - Assorted fixes for shmem helpers. qxl: - unpin qxl bos created as pinned when freeing them, and make ttm only warn once on this behavior. - Zero head.surface_id correctly in qxl. atyfb: - Use LCD management for atyfb on PPC_MAC. meson: - Shutdown kms poll helper in meson correctly. nouveau: - fix regression in bo syncing i915: - Wedge the GPU if command parser setup fails amdgpu: - Fix aux backlight control - Add a backlight override parameter - Various display fixes - PCIe DPM fix for vega - Polaris watermark fixes - Additional S0ix fix radeon: - Fix GEM regression - Fix AGP dependency handling" * tag 'drm-fixes-2021-03-12-1' of git://anongit.freedesktop.org/drm/drm: (33 commits) drm/nouveau: fix dma syncing for loops (v2) drm/i915: Wedge the GPU if command parser setup fails drm/compat: Clear bounce structures drm/shmem-helpers: vunmap: Don't put pages for dma-buf drm: meson_drv add shutdown function drm/shmem-helper: Don't remove the offset in vm_area_struct pgoff drm/shmem-helper: Check for purged buffers in fault handler qxl: Fix uninitialised struct field head.surface_id drm/ttm: Fix TTM page pool accounting drm/ttm: soften TTM warnings drm: Use USB controller's DMA mask when importing dmabufs MAINTAINERS: update drm bug reporting URL fbdev: atyfb: use LCD management functions for PPC_PMAC also fbdev: atyfb: always declare aty_{ld,st}_lcd() drm/qxl: fix lockdep issue in qxl_alloc_release_reserved drm/qxl: unpin release objects drm/fb-helper: only unmap if buffer not null drm/amdgpu: fix S0ix handling when the CONFIG_AMD_PMC=m drm/radeon: fix AGP dependency drm/radeon: also init GEM funcs in radeon_gem_prime_import_sg_table ...
errseq.c
// SPDX-License-Identifier: GPL-2.0
#include <linux/err.h>
#include <linux/bug.h>
#include <linux/atomic.h>
#include <linux/errseq.h>
#include <linux/log2.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 initialise their errseq_t variable.
* If the error has been "seen", new callers will not see an old error.
* If there is an unseen error in @eseq, the caller of this function will
* see it the next time it checks for an error.
*
* Context: Any context.
* Return: The current errseq value.
*/
errseq_t errseq_sample(errseq_t *eseq)
{
errseq_t old = READ_ONCE(*eseq);
/* If nobody has seen this error yet, then we can be the first. */
if (!(old & ERRSEQ_SEEN))
old = 0;
return old;
}
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);
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