Messages in this thread | | | Date | Thu, 3 Apr 2008 15:07:00 -0400 | From | Erez Zadok <> | Subject | Re: fs_stack/eCryptfs: remove 3rd arg of copy_attr_all, add locking to copy_inode_size |
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In message <20080403182001.GB30189@josefsipek.net>, "Josef 'Jeff' Sipek" writes: > On Wed, Apr 02, 2008 at 09:49:11PM -0400, Erez Zadok wrote: > ... > > +#if BITS_PER_LONG == 32 && defined(CONFIG_SMP) > > + spin_lock(&dst->i_lock); > > +#endif > > I think you need to check CONFIG_PREEMPT as well. > > Josef 'Jeff' Sipek.
I'm not sure if it's needed in case of CONFIG_PREEMPT. Anyone? The code for i_size_write (below), and the comment at the top of the function, suggest that the spinlock is needed only to prevent the lots seqcount.
/* * NOTE: unlike i_size_read(), i_size_write() does need locking around it * (normally i_mutex), otherwise on 32bit/SMP an update of i_size_seqcount * can be lost, resulting in subsequent i_size_read() calls spinning forever. */ static inline void i_size_write(struct inode *inode, loff_t i_size) { #if BITS_PER_LONG==32 && defined(CONFIG_SMP) write_seqcount_begin(&inode->i_size_seqcount); inode->i_size = i_size; write_seqcount_end(&inode->i_size_seqcount); #elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPT) preempt_disable(); inode->i_size = i_size; preempt_enable(); #else inode->i_size = i_size; #endif }
BTW, some time ago I reviewed all callers of i_size_write. I did so again just now, and the results were the same:
- a LOT of callers of i_size_write don't take any lock - some take another spinlock in a different data structure - those that do take the spinlock, do so unconditionally - only unionfs and fs/stack.c wrap the spinlock in
#if BITS_PER_LONG == 32 && defined(CONFIG_SMP)
Erez.
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