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Message-ID: <20160227152518.GB20887@joana>
Date: Sat, 27 Feb 2016 12:25:18 -0300
From: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
To: Emil Velikov <emil.l.velikov@...il.com>
Cc: Gustavo Padovan <gustavo@...ovan.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
devel@...verdev.osuosl.org, Daniel Stone <daniels@...labora.com>,
Daniel Vetter <daniel.vetter@...ll.ch>,
Riley Andrews <riandrews@...roid.com>,
ML dri-devel <dri-devel@...ts.freedesktop.org>,
"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
Arve Hjønnevåg <arve@...roid.com>,
John Harrison <John.C.Harrison@...el.com>
Subject: Re: [PATCH] staging/android: refactor SYNC_IOC_FILE_INFO
Hi Emil,
2016-02-27 Emil Velikov <emil.l.velikov@...il.com>:
> Hi Gustavo,
>
> On 26 February 2016 at 21:00, Gustavo Padovan <gustavo@...ovan.org> wrote:
> > From: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
> >
> > Change SYNC_IOC_FILE_INFO behaviour to avoid future API breaks and
> > optimize buffer allocation. In the new approach the ioctl needs to be called
> > twice to retrieve the array of fence_infos pointed by info->sync_fence_info.
> >
> I might have misunderstood things but I no one says you "need" to call
> it twice - you can just request a "random" amount of fences_info. Upon
> return (if num_fences was non zero) it will report how many fence_info
> were retrieved.
Right, I don't see any problem doing it in one request, I just didn't
think about that in the new proposal. I'll update the code and commit
message accordinly.
>
> > The first call should pass num_fences = 0, the kernel will then fill
> > info->num_fences. Userspace receives back the number of fences and
> > allocates a buffer size num_fences * sizeof(struct sync_fence_info) on
> > info->sync_fence_info.
> >
> > It then call the ioctl again passing num_fences received in info->num_fences.
> "calls"
>
> > The kernel checks if info->num_fences > 0 and if yes it fill
> > info->sync_fence_info with an array containing all fence_infos.
> >
> The above sentence sounds a bit strange. I believe you meant to say
> something like "Then the kernel fills the fence_infos array with data.
> One should read back the actual number from info->num_fences." ?
>
> > info->len now represents the length of the buffer sync_fence_info points
> > to.
> Now that I think about it, I'm wondering if there'll be a case where
> len != info->num_fences * sizeof(struct sync_file_info). If that's not
> possible one could just drop len and nicely simplify things.
>
> > Also, info->sync_fence_info was converted to __u64 pointer.
> >
> ... pointer to prevent 32bit compatibility issues.
>
> > An example userspace code would be:
> >
> > struct sync_file_info *info;
> > int err, size, num_fences;
> >
> > info = malloc(sizeof(*info));
> >
> > memset(info, 0, sizeof(*info));
> >
> > err = ioctl(fd, SYNC_IOC_FILE_INFO, info);
> > num_fences = info->num_fences;
> >
> > if (num_fences) {
> > memset(info, 0, sizeof(*info));
> > size = sizeof(struct sync_fence_info) * num_fences;
> > info->len = size;
> > info->num_fences = num_fences;
> > info->sync_fence_info = (uint64_t) calloc(num_fences,
> > sizeof(struct sync_fence_info));
> >
> > err = ioctl(fd, SYNC_IOC_FILE_INFO, info);
> > }
> >
> > v2: fix fence_info memory leak
> >
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
> > ---
> > drivers/staging/android/sync.c | 52 +++++++++++++++++++++++++++++--------
> > drivers/staging/android/uapi/sync.h | 9 +++----
> > 2 files changed, 45 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
> > index dc5f382..2379f23 100644
> > --- a/drivers/staging/android/sync.c
> > +++ b/drivers/staging/android/sync.c
> > @@ -502,21 +502,22 @@ static int sync_fill_fence_info(struct fence *fence, void *data, int size)
> > static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
> > unsigned long arg)
> > {
> > - struct sync_file_info *info;
> > + struct sync_file_info in, *info;
> > + struct sync_fence_info *fence_info = NULL;
> > __u32 size;
> > __u32 len = 0;
> > int ret, i;
> >
> > - if (copy_from_user(&size, (void __user *)arg, sizeof(size)))
> > + if (copy_from_user(&in, (void __user *)arg, sizeof(*info)))
> s/*info/in/
>
> > return -EFAULT;
> >
> > - if (size < sizeof(struct sync_file_info))
> > - return -EINVAL;
> > + if (in.status || strcmp(in.name, "\0"))
> Afaict these two are outputs, so we should be checking them ?
Hmm. Maybe not.
>
> > + return -EFAULT;
> >
> As originally, input validation should return -EINVAL on error.
>
>
> > - if (size > 4096)
> > - size = 4096;
> > + if (in.num_fences && !in.sync_fence_info)
> > + return -EFAULT;
> >
> Ditto.
>
> > - info = kzalloc(size, GFP_KERNEL);
> > + info = kzalloc(sizeof(*info), GFP_KERNEL);
> > if (!info)
> > return -ENOMEM;
> >
> > @@ -525,14 +526,33 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
> > if (info->status >= 0)
> > info->status = !info->status;
> >
> > - info->num_fences = sync_file->num_fences;
> > + /*
> > + * Passing num_fences = 0 means that userspace want to know how
> > + * many fences are in the sync_file to be able to allocate a buffer to
> > + * fit all sync_fence_infos and call the ioctl again with the buffer
> > + * assigned to info->sync_fence_info. The second call pass the
> > + * num_fences value received in the first call.
> > + */
> > + if (!in.num_fences)
> > + goto no_fences;
> > +
> We should clamp in.num_fences to min2(in.num_fences,
> sync_file->num_fences) and use it over sync_file->num_fences though
> the rest of the function. Or just bail out when the two are not the
> same.
>
> Depends on what the planned semantics are. Fwiw I'm leaning towards the former.
If num_fences received is smaller than the actual num_fences I think we
should fails, otherwise we should just fill the buffer with all
fence_infos...
>
> > + size = sync_file->num_fences * sizeof(*fence_info);
> > + if (in.len != size) {
> > + ret = -EFAULT;
> EINVAL or just drop len from the struct.
...so this check now would be in.len < size.
>
> > + goto out;
> > + }
> >
> > - len = sizeof(struct sync_file_info);
> > + fence_info = kzalloc(size, GFP_KERNEL);
> > + if (!fence_info) {
> > + ret = -ENOMEM;
> > + goto out;
> > + }
> >
> > for (i = 0; i < sync_file->num_fences; ++i) {
> > struct fence *fence = sync_file->cbs[i].fence;
> >
> > - ret = sync_fill_fence_info(fence, (u8 *)info + len, size - len);
> > + ret = sync_fill_fence_info(fence, (u8 *)fence_info + len,
> A few comments about sync_fill_fence_info()
> - Internal function so make the second argument of the correct type -
> struct sync_fence_info *
> - Drop the third argument size, as that one is always sizeof(sync_fence_info).
> - Remove the size checking in the same function and make its return type void
>
> Then one can simplify this loop even further :-)
Sounds good to me.
>
> > + size - len);
> >
> > if (ret < 0)
> > goto out;
> > @@ -540,14 +560,24 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
> > len += ret;
> > }
> >
> > + if (copy_to_user((void __user *)in.sync_fence_info, fence_info, size)) {
> > + ret = -EFAULT;
> > + goto out;
> > + }
> > +
> > info->len = len;
> > + info->sync_fence_info = (__u64) in.sync_fence_info;
> Why the cast ?
>
> > +
> > +no_fences:
> > + info->num_fences = sync_file->num_fences;
> >
> > - if (copy_to_user((void __user *)arg, info, len))
> > + if (copy_to_user((void __user *)arg, info, sizeof(*info)))
> Don't know if we should be returning (copying) any other information
> but info->num_fences in case of "no_fences". In case it's not clear -
> I'm thinking about the data we already have in in info->name and
> info->status.
Userspace might want to know all info about the sync_file but
sync_fence_info.
Gustavo
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