[bug report] shmem: quota support

[Dan Carpenter <dan.carpenter@linaro.org>]

Hello Carlos Maiolino,

The patch 9a9f8f590f6d: "shmem: quota support" from Jul 25, 2023
(linux-next), leads to the following Smatch static checker warning:

	fs/quota/dquot.c:1271 flush_warnings()
	warn: sleeping in atomic context

fs/quota/dquot.c
    1261 static void flush_warnings(struct dquot_warn *warn)
    1262 {
    1263         int i;
    1264 
    1265         for (i = 0; i < MAXQUOTAS; i++) {
    1266                 if (warn[i].w_type == QUOTA_NL_NOWARN)
    1267                         continue;
    1268 #ifdef CONFIG_PRINT_QUOTA_WARNING
    1269                 print_warning(&warn[i]);
    1270 #endif
--> 1271                 quota_send_warning(warn[i].w_dq_id,
    1272                                    warn[i].w_sb->s_dev, warn[i].w_type);

The quota_send_warning() function does GFP_NOFS allocations, which don't
touch the fs but can still sleep.  GFP_ATOMIC or GFP_NOWAIT don't sleep.

    1273         }
    1274 }

The call trees that Smatch is worried about are listed.  The "disables
preempt" functions take the spin_lock_irq(&info->lock) before calling
shmem_recalc_inode().

shmem_charge() <- disables preempt
shmem_uncharge() <- disables preempt
shmem_undo_range() <- disables preempt
shmem_getattr() <- disables preempt
shmem_writepage() <- disables preempt
shmem_set_folio_swapin_error() <- disables preempt
shmem_swapin_folio() <- disables preempt
shmem_get_folio_gfp() <- disables preempt
-> shmem_recalc_inode()
   -> shmem_inode_unacct_blocks()
      -> dquot_free_block_nodirty()
         -> dquot_free_space_nodirty()
            -> __dquot_free_space()
               -> flush_warnings()

regards,
dan carpenter