ports/140648 multimedia/vlc causes a panic if media files are on msdosfs

[Doug Barton]

Kostik Belousov wrote:
> On Thu, Nov 19, 2009 at 02:30:33PM -0800, Doug Barton wrote:
>> Please see http://www.freebsd.org/cgi/query-pr.cgi?pr=140648 for more
>> information, including a trace.
>>
>> There is also some evidence that the same problem is triggered by
>> accessing files on an NTFS partition. The VLC folks have suggested
>> that the problem may be related to threading.
> 
> This is because msdosfs and ntfs are not mpsafe, and it seems that
> VLC using recently added F_RDAHEAD/F_READAHEAD fcntls.
> 
> Please try this.
> 
> diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
> index 434f54a..676de65 100644
> --- a/sys/kern/kern_descrip.c
> +++ b/sys/kern/kern_descrip.c
> @@ -718,14 +718,15 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
>  			do {
>  				new = old = fp->f_flag;
>  				new |= FRDAHEAD;
> -			} while (atomic_cmpset_rel_int(&fp->f_flag, old, new) == 0);
> +			} while (!atomic_cmpset_rel_int(&fp->f_flag, old, new));
>  readahead_vnlock_fail:
>  			VFS_UNLOCK_GIANT(vfslocked);
> +			vfslocked = 0;
>  		} else {
>  			do {
>  				new = old = fp->f_flag;
>  				new &= ~FRDAHEAD;
> -			} while (atomic_cmpset_rel_int(&fp->f_flag, old, new) == 0);
> +			} while (!atomic_cmpset_rel_int(&fp->f_flag, old, new));
>  		}
>  		fdrop(fp, td);
>  		break;

Voila! Thanks.

Doug

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