diff options
| -rw-r--r-- | MAINTAINERS | 6 | ||||
| -rw-r--r-- | include/linux/errseq.h | 19 | ||||
| -rw-r--r-- | lib/Makefile | 2 | ||||
| -rw-r--r-- | lib/errseq.c | 208 |
4 files changed, 234 insertions, 1 deletions
diff --git a/MAINTAINERS b/MAINTAINERS index 9e984645c4b0..c2465dc21946 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -4999,6 +4999,12 @@ T: git git://git.kernel.org/pub/scm/linux/kernel/git/kristoffer/linux-hpc.git F: drivers/video/fbdev/s1d13xxxfb.c F: include/video/s1d13xxxfb.h +ERRSEQ ERROR TRACKING INFRASTRUCTURE +M: Jeff Layton <jlayton@poochiereds.net> +S: Maintained +F: lib/errseq.c +F: include/linux/errseq.h + ET131X NETWORK DRIVER M: Mark Einon <mark.einon@gmail.com> S: Odd Fixes diff --git a/include/linux/errseq.h b/include/linux/errseq.h new file mode 100644 index 000000000000..9e0d444ac88d --- /dev/null +++ b/include/linux/errseq.h @@ -0,0 +1,19 @@ +#ifndef _LINUX_ERRSEQ_H +#define _LINUX_ERRSEQ_H + +/* See lib/errseq.c for more info */ + +typedef u32 errseq_t; + +errseq_t __errseq_set(errseq_t *eseq, int err); +static inline void errseq_set(errseq_t *eseq, int err) +{ + /* Optimize for the common case of no error */ + if (unlikely(err)) + __errseq_set(eseq, err); +} + +errseq_t errseq_sample(errseq_t *eseq); +int errseq_check(errseq_t *eseq, errseq_t since); +int errseq_check_and_advance(errseq_t *eseq, errseq_t *since); +#endif diff --git a/lib/Makefile b/lib/Makefile index 0166fbc0fa81..519782d9ca3f 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -41,7 +41,7 @@ obj-y += bcd.o div64.o sort.o parser.o debug_locks.o random32.o \ gcd.o lcm.o list_sort.o uuid.o flex_array.o iov_iter.o clz_ctz.o \ bsearch.o find_bit.o llist.o memweight.o kfifo.o \ percpu-refcount.o percpu_ida.o rhashtable.o reciprocal_div.o \ - once.o refcount.o usercopy.o + once.o refcount.o usercopy.o errseq.o obj-y += string_helpers.o obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o obj-y += hexdump.o diff --git a/lib/errseq.c b/lib/errseq.c new file mode 100644 index 000000000000..841fa24e6e00 --- /dev/null +++ b/lib/errseq.c @@ -0,0 +1,208 @@ +#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 + * + * 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. + * + * Most callers will want to use the errseq_set inline wrapper to efficiently + * handle the common case where err is 0. + * + * We do return an errseq_t here, 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. + */ +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. + * + * Returns 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. + */ +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); |