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aio: Fix more synchronization issues in aio_biowakeup.

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- Use atomic_store to set job->error.  atomic_set does an or
  operation, not assignment.

- Use refcount_* to manage job->nbio.

  This ensures proper memory barriers are present so that the last bio
  won't see a possibly stale value of job->error.

- Don't re-read job->error after reading it via atomic_load.

Reported by:	markj (1)
Reviewed by:	mjg, markj
Differential Revision:	https://reviews.freebsd.org/D38611
This commit is contained in:
John Baldwin 2023-02-15 13:32:52 -08:00
parent 059320b8c8
commit 98844e99d4
2 changed files with 7 additions and 6 deletions
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11
sys/kern/vfs_aio.c
View File

@ -1281,7 +1281,7 @@ aio_qbio(struct proc *p, struct kaiocb *job)
}
bios = malloc(sizeof(struct bio *) * iovcnt, M_TEMP, M_WAITOK);
atomic_store_int(&job->nbio, iovcnt);
refcount_init(&job->nbio, iovcnt);
for (i = 0; i < iovcnt; i++) {
struct vm_page** pages;
struct bio *bp;
@ -2489,15 +2489,16 @@ aio_biowakeup(struct bio *bp)
* error of whichever failed bio completed last.
*/
if (flags & BIO_ERROR)
atomic_set_int(&job->error, bio_error);
atomic_store_int(&job->error, bio_error);
if (opcode & LIO_WRITE)
atomic_add_int(&job->outblock, nblks);
else
atomic_add_int(&job->inblock, nblks);
if (atomic_fetchadd_int(&job->nbio, -1) == 1) {
if (atomic_load_int(&job->error))
aio_complete(job, -1, job->error);
if (refcount_release(&job->nbio)) {
bio_error = atomic_load_int(&job->error);
if (bio_error != 0)
aio_complete(job, -1, bio_error);
else
aio_complete(job, atomic_load_long(&job->nbytes), 0);
}

2
sys/sys/aio.h
View File

@ -151,7 +151,7 @@ struct kaiocb {
aio_handle_fn_t *handle_fn; /* (c) backend handle function */
union { /* Backend-specific data fields */
struct { /* BIO backend */
int nbio; /* Number of remaining bios */
volatile u_int nbio; /* Number of remaining bios */
int error; /* Worst error of all bios */
long nbytes; /* Bytes completed so far */
};