On 04/25/2012 11:39 AM, Jan Schmidt wrote:
> Hi Goffredo,
>
> On 24.04.2012 20:43, Goffredo Baroncelli wrote:
>> I was giving a look to the function scrub_fs_info( ), and to me it seems
>> that could be a potential file handle leaking problem.
>
> It's only a single fd that's closed upon exit, but anyway...
Ironically, quite often the problem doesn't exist at all, because if I
1) open a file descriptr
2) close the file descriptr
3) open a new file descriptor
For 1) and 2) the kernel re-use the same file descriptor.
However I think that the scrub_fs_info() could be a more generic
function (not only scrub related) which could be reused in more places.
So a more polite behaviour it is needed.
>
>> In fact:
>>
>> static int scrub_fs_info(int fd, char *path,
>> struct btrfs_ioctl_fs_info_args *fi_args,
>> struct btrfs_ioctl_dev_info_args **di_ret)
>> {
>>
>> [...]
>>
>> ret = ioctl(fd, BTRFS_IOC_FS_INFO, fi_args);
>> if (ret && errno == EINVAL) {
>> /* path is no mounted btrfs. try if it's a device */
>> [...]
>> close(fd); <--- Here the
>> file handle is
>> closed
>>
>> fd = open_file_or_dir(mp); <--- then it is
>> re-opened
>> if (fd < 0)
>> return -errno;
>> } else if (ret) {
>> return -errno;
>> }
>> [...]
>>
>> But in the rest of the function:
>> a) the file handle is not closed
>> b) the (new) file handle isn't returned
>
> You're right, that's unintended. I admit that I haven't tested passing a
> device instead of a mountpoint that much.
>
>> The function "scrub_fs_info()" is called from the functions
>> 1) cmd_scrub_status(), which doesn't use the file handle after the call
>> to the cmd_scrub_status() [except for a close()]. So no problem at all.
>> 2) scrub_start(), which uses the file handle after the call to the
>> cmd_scrub_status() functions.
>>
>> My suggestions is to change scrub_fs_info() to accept only the path.
>> Then it open (and closes) its own (and private) the file descriptor.
>>
>> Instead scrub_start(), opens a file descriptor after the call to the
>> scrub_fs_info() function.
>>
>> What do you think ?
>
> My naive approach would be to pass an int * to scrub_fs_info. One has to
> make sure that scrub_start doesn't rely on "fdmnt" not being updated.
> After skipping through it, I think it expects "fdmnt" to be an open fd,
> and it looks like it should be exactly the one used in scrub_fs_info.
> Would you like to test the int * approach?
Frankly speaking, I don't like the idea that scrub_fs_info() could
change the file descriptor. I think that it is not good design.
I would like to suggest the following options:
1) scrub_fs_info() opens a file descriptor on the basis of the path
parameters. And then it returns this file descriptor (or via return or
via a int * parameters)
or
2) we move the re-open logic outside the function itself. So
scrub_start() don't need to change the file descriptor.
I prefer the options #2, also because this is a quite common problem: we
can create a generic function which returns a good file descriptor when
a filesystem path and/or the device is passed
What do you think ?
Finally I will take in account your suggestion regarding the spacing.
BR
G.Baroncelli
>
>> BR
>> G.Baroncelli
>>
>> You can pull the patch below from
>>
>> http://cassiopea.homelinux.net/git/btrfs-progs-unstable.git
>>
>> branch
>>
>> fd-leaking
>>
>> -----
>>
>> diff --git a/cmds-scrub.c b/cmds-scrub.c
>> index c4503f4..486768c 100644
>> --- a/cmds-scrub.c
>> +++ b/cmds-scrub.c
>> @@ -979,19 +979,26 @@ static int scrub_device_info(int fd, u64 devid,
>> return ret ? -errno : 0;
>> }
>>
>> -static int scrub_fs_info(int fd, char *path,
>> +static int scrub_fs_info( char *path,
> ^
> Apart from my proposed solution, the spacing in your patch doesn't
> follow the style guide. No space here.
>
>> struct btrfs_ioctl_fs_info_args *fi_args,
>> struct btrfs_ioctl_dev_info_args **di_ret)
>> {
>> int ret = 0;
>> int ndevs = 0;
>> int i = 1;
>> + int fd;
>> struct btrfs_fs_devices *fs_devices_mnt = NULL;
>> struct btrfs_ioctl_dev_info_args *di_args;
>> char mp[BTRFS_PATH_NAME_MAX + 1];
>>
>> memset(fi_args, 0, sizeof(*fi_args));
>>
>> + fd = open_file_or_dir(path);
>> + if (fd < 0) {
>> + fprintf(stderr, "ERROR: can't access to '%s'\n", path);
>> + return -1;
>> + }
>> +
>> ret = ioctl(fd, BTRFS_IOC_FS_INFO, fi_args);
>> if (ret && errno == EINVAL) {
>> /* path is no mounted btrfs. try if it's a device */
>> @@ -1010,28 +1017,36 @@ static int scrub_fs_info(int fd, char *path,
>> if (fd < 0)
>> return -errno;
>> } else if (ret) {
>> + close(fd);
>> return -errno;
>> }
>>
>> - if (!fi_args->num_devices)
>> + if (!fi_args->num_devices){
> ^
> space here
>
>> + close(fd);
>> return 0;
>> + }
>>
>> di_args = *di_ret = malloc(fi_args->num_devices * sizeof(*di_args));
>> - if (!di_args)
>> + if (!di_args){
> ^
> space here
>
>> + close(fd);
>> return -errno;
>> + }
>>
>> for (; i <= fi_args->max_id; ++i) {
>> BUG_ON(ndevs >= fi_args->num_devices);
>> ret = scrub_device_info(fd, i, &di_args[ndevs]);
>> if (ret == -ENODEV)
>> continue;
>> - if (ret)
>> + if (ret){
> ^
> space here
>
>> + close(fd);
>> return ret;
>> + }
>> ++ndevs;
>> }
>>
>> BUG_ON(ndevs == 0);
>>
>> + close(fd);
>> return 0;
>> }
>>
>> @@ -1155,7 +1170,7 @@ static int scrub_start(int argc, char **argv, int
>> resume)
>> return 12;
>> }
>>
>> - ret = scrub_fs_info(fdmnt, path, &fi_args, &di_args);
>> + ret = scrub_fs_info(path, &fi_args, &di_args);
>> if (ret) {
>> ERR(!do_quiet, "ERROR: getting dev info for scrub failed: "
>> "%s\n", strerror(-ret));
>> @@ -1586,7 +1601,6 @@ static int cmd_scrub_status(int argc, char **argv)
>> .sun_family = AF_UNIX,
>> };
>> int ret;
>> - int fdmnt;
>> int i;
>> int print_raw = 0;
>> int do_stats_per_dev = 0;
>> @@ -1615,13 +1629,7 @@ static int cmd_scrub_status(int argc, char **argv)
>>
>> path = argv[optind];
>>
>> - fdmnt = open_file_or_dir(path);
>> - if (fdmnt < 0) {
>> - fprintf(stderr, "ERROR: can't access to '%s'\n", path);
>> - return 12;
>> - }
>> -
>> - ret = scrub_fs_info(fdmnt, path, &fi_args, &di_args);
>> + ret = scrub_fs_info(path, &fi_args, &di_args);
>> if (ret) {
>> fprintf(stderr, "ERROR: getting dev info for scrub failed: "
>> "%s\n", strerror(-ret));
>> @@ -1698,7 +1706,6 @@ static int cmd_scrub_status(int argc, char **argv)
>> out:
>> free_history(past_scrubs);
>> free(di_args);
>> - close(fdmnt);
>> if (fdres > -1)
>> close(fdres);
>>
>>
>>
>>
>>
>>
>
> Thanks!
> -Jan
> .
>
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