On 2013/3/21 12:48, Ming Lei wrote: > On Thu, Mar 21, 2013 at 11:28 AM, Li Zefan <lize...@huawei.com> wrote: >> On 2013/3/21 11:17, Ming Lei wrote: >>> On Thu, Mar 21, 2013 at 10:41 AM, Li Zefan <lize...@huawei.com> wrote: >>>> >>>> In fact the same race exists between readdir() and read()/write()... >>> >>> Fortunately, no read()/write() are implemented on sysfs directory, :-) >>> >> >> That's irrelevant... > > As far as sysfs is concerned, the filp->f_ops can't be changed in > read/write path. >
Yes, it can...As I said, it's irrelevant, because it's vfs that changes file->f_pos. SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count) { struct fd f = fdget(fd); ssize_t ret = -EBADF; if (f.file) { loff_t pos = file_pos_read(f.file); <--- read f_pos ret = vfs_read(f.file, buf, count, &pos); <--- return -EISDIR file_pos_write(f.file, pos); <--- write f_pos fdput(f); } return ret; } >> >> See my report: >> >> https://patchwork.kernel.org/patch/2160771/ > > Yes, I know there might be some mess after the commit ef3d0fd2 > (vfs: do (nearly) lockless generic_file_llseek). > > Also looks it has been stated in Documentation/filesystems/Locking: > > ->llseek() locking has moved from llseek to the individual llseek > implementations. If your fs is not using generic_file_llseek, you > need to acquire and release the appropriate locks in your ->llseek(). > For many filesystems, it is probably safe to acquire the inode > mutex or just to use i_size_read() instead. > Note: this does not protect the file->f_pos against concurrent modifications > since this is something the userspace has to take care about. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/