Re: [PATCH vfs.tmpfs] shmem: move spinlock into shmem_recalc_inode() to fix quota support

[Jan Kara <jack@suse.cz>]

On Thu 03-08-23 22:46:11, Hugh Dickins wrote:
> Commit "shmem: fix quota lock nesting in huge hole handling" was not so
> good: Smatch caught shmem_recalc_inode()'s shmem_inode_unacct_blocks()
> descending into quota_send_warning(): where blocking GFP_NOFS is used,
> yet shmem_recalc_inode() is called holding the shmem inode's info->lock.
> 
> Yes, both __dquot_alloc_space() and __dquot_free_space() are commented
> "This operation can block, but only after everything is updated" - when
> calling flush_warnings() at the end - both its print_warning() and its
> quota_send_warning() may block.
> 
> Rework shmem_recalc_inode() to take the shmem inode's info->lock inside,
> and drop it before calling shmem_inode_unacct_blocks().
> 
> And why were the spin_locks disabling interrupts?  That was just a relic
> from when shmem_charge() and shmem_uncharge() were called while holding
> i_pages xa_lock: stop disabling interrupts for info->lock now.
> 
> To help stop me from making the same mistake again, add a might_sleep()
> into shmem_inode_acct_block() and shmem_inode_unacct_blocks(); and those
> functions have grown, so let the compiler decide whether to inline them.
> 
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/linux-fsdevel/ffd7ca34-7f2a-44ee-b05d-b54d920ce076@moroto.mountain/
> Signed-off-by: Hugh Dickins <hughd@google.com>

Thanks for the fix Hugh! The patch looks good to me so feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

(FWIW for shmem code).
								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR