diff options
| author | Jan Kara <jack@suse.cz> | 2020-07-15 14:06:21 +0200 |
|---|---|---|
| committer | Jan Kara <jack@suse.cz> | 2020-07-15 15:23:28 +0200 |
| commit | 47aaabdedf366ac5894c7fddec388832f0d8193e (patch) | |
| tree | 6e57adb2dc53d571eaa165a8e2810cef00a90332 /fs/notify | |
| parent | 0bddd227f3dc55975e2b8dfa7fc6f959b062a2c7 (diff) | |
| download | linux-47aaabdedf366ac5894c7fddec388832f0d8193e.tar.gz | |
fanotify: Avoid softlockups when reading many events
When user provides large buffer for events and there are lots of events available, we can try to copy them all to userspace without scheduling which can softlockup the kernel (furthermore exacerbated by the contention on notification_lock). Add a scheduling point after copying each event. Note that usually the real underlying problem is the cost of fanotify event merging and the resulting contention on notification_lock but this is a cheap way to somewhat reduce the problem until we can properly address that. Reported-by: Francesco Ruggeri <fruggeri@arista.com> Link: https://lore.kernel.org/lkml/20200714025417.A25EB95C0339@us180.sjc.aristanetworks.com Reviewed-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'fs/notify')
| -rw-r--r-- | fs/notify/fanotify/fanotify_user.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index 63b5dffdca9e..d7f63aeca992 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -412,6 +412,11 @@ static ssize_t fanotify_read(struct file *file, char __user *buf, add_wait_queue(&group->notification_waitq, &wait); while (1) { + /* + * User can supply arbitrarily large buffer. Avoid softlockups + * in case there are lots of available events. + */ + cond_resched(); event = get_one_event(group, count); if (IS_ERR(event)) { ret = PTR_ERR(event); |