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poll: use fget_unlocked or fget_only_user when feasible

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This follows select by eleminating the use of filedesc lock.
This is a win for single-threaded processes and a mixed bag for others
as at small concurrency it is faster to take the lock instead of
refing/unrefing each file descriptor.

Nonetheless, removal of shared lock usage is a step towards a
mtx-protected fd table.
This commit is contained in:
Mateusz Guzik 2021-01-29 00:52:08 +01:00
parent 6affe1b712
commit 45e1f85414
1 changed files with 24 additions and 51 deletions
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75
sys/kern/sys_generic.c
View File

@ -1547,49 +1547,6 @@ sys_ppoll(struct thread *td, struct ppoll_args *uap)
return (kern_poll(td, uap->fds, uap->nfds, tsp, ssp));
}
#ifdef CAPABILITIES
static int
poll_fget(struct filedesc *fdp, int fd, struct file **fpp)
{
const struct filedescent *fde;
const struct fdescenttbl *fdt;
const cap_rights_t *haverights;
struct file *fp;
int error;
if (__predict_false(fd >= fdp->fd_nfiles))
return (EBADF);
fdt = fdp->fd_files;
fde = &fdt->fdt_ofiles[fd];
fp = fde->fde_file;
if (__predict_false(fp == NULL))
return (EBADF);
haverights = cap_rights_fde_inline(fde);
error = cap_check_inline(haverights, &cap_event_rights);
if (__predict_false(error != 0))
return (EBADF);
*fpp = fp;
return (0);
}
#else
static int
poll_fget(struct filedesc *fdp, int fd, struct file **fpp)
{
struct file *fp;
if (__predict_false(fd >= fdp->fd_nfiles))
return (EBADF);
fp = fdp->fd_ofiles[fd].fde_file;
if (__predict_false(fp == NULL))
return (EBADF);
*fpp = fp;
return (0);
}
#endif
static int
pollrescan(struct thread *td)
{
@ -1600,12 +1557,13 @@ pollrescan(struct thread *td)
struct filedesc *fdp;
struct file *fp;
struct pollfd *fd;
int n;
int n, error;
bool only_user;
n = 0;
fdp = td->td_proc->p_fd;
stp = td->td_sel;
FILEDESC_SLOCK(fdp);
only_user = FILEDESC_IS_ONLY_USER(fdp);
STAILQ_FOREACH_SAFE(sfp, &stp->st_selq, sf_link, sfn) {
fd = (struct pollfd *)sfp->sf_cookie;
si = sfp->sf_si;
@ -1613,7 +1571,11 @@ pollrescan(struct thread *td)
/* If the selinfo wasn't cleared the event didn't fire. */
if (si != NULL)
continue;
if (poll_fget(fdp, fd->fd, &fp) != 0) {
if (only_user)
error = fget_only_user(fdp, fd->fd, &cap_event_rights, &fp);
else
error = fget_unlocked(fdp, fd->fd, &cap_event_rights, &fp);
if (__predict_false(error != 0)) {
fd->revents = POLLNVAL;
n++;
continue;
@ -1623,10 +1585,13 @@ pollrescan(struct thread *td)
* POLLERR if appropriate.
*/
fd->revents = fo_poll(fp, fd->events, td->td_ucred, td);
if (only_user)
fput_only_user(fdp, fp);
else
fdrop(fp, td);
if (fd->revents != 0)
n++;
}
FILEDESC_SUNLOCK(fdp);
stp->st_flags = 0;
td->td_retval[0] = n;
return (0);
@ -1658,17 +1623,22 @@ pollscan(struct thread *td, struct pollfd *fds, u_int nfd)
{
struct filedesc *fdp;
struct file *fp;
int i, n;
int i, n, error;
bool only_user;
n = 0;
fdp = td->td_proc->p_fd;
FILEDESC_SLOCK(fdp);
only_user = FILEDESC_IS_ONLY_USER(fdp);
for (i = 0; i < nfd; i++, fds++) {
if (fds->fd < 0) {
fds->revents = 0;
continue;
}
if (poll_fget(fdp, fds->fd, &fp) != 0) {
if (only_user)
error = fget_only_user(fdp, fds->fd, &cap_event_rights, &fp);
else
error = fget_unlocked(fdp, fds->fd, &cap_event_rights, &fp);
if (__predict_false(error != 0)) {
fds->revents = POLLNVAL;
n++;
continue;
@ -1680,6 +1650,10 @@ pollscan(struct thread *td, struct pollfd *fds, u_int nfd)
selfdalloc(td, fds);
fds->revents = fo_poll(fp, fds->events,
td->td_ucred, td);
if (only_user)
fput_only_user(fdp, fp);
else
fdrop(fp, td);
/*
* POSIX requires POLLOUT to be never
* set simultaneously with POLLHUP.
@ -1690,7 +1664,6 @@ pollscan(struct thread *td, struct pollfd *fds, u_int nfd)
if (fds->revents != 0)
n++;
}
FILEDESC_SUNLOCK(fdp);
td->td_retval[0] = n;
return (0);
}