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Subject[PATCH 18/23] vfs: Teach epoll to use file_hotplug_lock
From: Eric W. Biederman <ebiederm@maxwell.aristanetworks.com>

Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
---
fs/eventpoll.c | 39 ++++++++++++++++++++++++++++++++-------
1 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index a89f370..eabb167 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -627,8 +627,13 @@ static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
struct epitem *epi, *tmp;

list_for_each_entry_safe(epi, tmp, head, rdllink) {
- if (epi->ffd.file->f_op->poll(epi->ffd.file, NULL) &
- epi->event.events)
+ int events = DEAD_POLLMASK;
+
+ if (file_hotplug_read_trylock(epi->ffd.file)) {
+ events = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
+ file_hotplug_read_unlock(epi->ffd.file);
+ }
+ if (events & epi->event.events)
return POLLIN | POLLRDNORM;
else {
/*
@@ -1060,8 +1065,12 @@ static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,

list_del_init(&epi->rdllink);

- revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL) &
- epi->event.events;
+ revents = DEAD_POLLMASK;
+ if (file_hotplug_read_trylock(epi->ffd.file)) {
+ revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
+ file_hotplug_read_unlock(epi->ffd.file);
+ }
+ revents &= epi->event.events;

/*
* If the event mask intersect the caller-requested one,
@@ -1248,10 +1257,17 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
if (!tfile)
goto error_fput;

+ error = -EIO;
+ if (!file_hotplug_read_trylock(file))
+ goto error_tgt_fput;
+
+ if (!file_hotplug_read_trylock(tfile))
+ goto error_file_unlock;
+
/* The target file descriptor must support poll */
error = -EPERM;
if (!tfile->f_op || !tfile->f_op->poll)
- goto error_tgt_fput;
+ goto error_tgt_unlock;

/*
* We have to check that the file structure underneath the file descriptor
@@ -1260,7 +1276,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
*/
error = -EINVAL;
if (file == tfile || !is_file_epoll(file))
- goto error_tgt_fput;
+ goto error_tgt_unlock;

/*
* At this point it is safe to assume that the "private_data" contains
@@ -1302,6 +1318,10 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
}
mutex_unlock(&ep->mtx);

+error_tgt_unlock:
+ file_hotplug_read_unlock(tfile);
+error_file_unlock:
+ file_hotplug_read_unlock(file);
error_tgt_fput:
fput(tfile);
error_fput:
@@ -1338,13 +1358,16 @@ SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
if (!file)
goto error_return;

+ error = -EIO;
+ if (!file_hotplug_read_trylock(file))
+ goto error_fput;
/*
* We have to check that the file structure underneath the fd
* the user passed to us _is_ an eventpoll file.
*/
error = -EINVAL;
if (!is_file_epoll(file))
- goto error_fput;
+ goto error_unlock;

/*
* At this point it is safe to assume that the "private_data" contains
@@ -1355,6 +1378,8 @@ SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
/* Time to fish for events ... */
error = ep_poll(ep, events, maxevents, timeout);

+error_unlock:
+ file_hotplug_read_unlock(file);
error_fput:
fput(file);
error_return:
--
1.6.3.1.54.g99dd.dirty


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