On Wednesday 18 November 2009, Jamie Lokier wrote: > Alan Cox wrote: > > > Using the BKL in llseek() does not protect the inode's i_size from > > > modification since the i_size is protected by a seqlock nowadays. Since > > > default_llseek() is already using the i_size_read() wrapper it is not the > > > BKL which is serializing the access here. > > > The access to file->f_pos is not protected by the BKL either since its > > > access in vfs_write()/vfs_read() is not protected by any lock. If the BKL > > > is not protecting anything here it can clearly get removed. > > > > No. Your logic is flawed > > > > The BKL is protected something here - it protects the change of offset > > with respect to other BKL users within drivers. The question is what if > > anything in any other driver code depends upon the BKL and uses it to > > protect f_pos. Probably very little if anything but a grep for f_pos > > through the drivers might not be a bad idea before assuming this. Very > > few touch f_pos except in their own llseek method. > > Of course, drivers shouldn't be using f_pos outside their llseek > method, as they should all behave the same with pread/pwrite as with > llseek+read/write. > > Is that mistaken? There are drivers touching f_pos in ioctl() methods, which is vaguely reasonable. There are also driver touching it in their read()/write() methods, which has no effect whatsoever. I started grepping through the kernel trying to find any instances of the first case that uses the BKL, but I only found three instances of the second case and got heavily demotivated by that. Arnd <>< -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
