EXT3: problem with copy_from_user inside a transaction

[Andrey Savochkin]

Hi Andrew,

filemap_copy_from_user() between prepare_write() and commit_write()
appears to be a problem for ext3.

prepare_write() starts a transaction, and if filemap_copy_from_user() causes
a page fault, we'll have
 - order violation with mmap_sem taken inside a transaction (possible
   deadlocks),
 - __GFP_FS memory allocation with all re-entrancy problems (e.g.,
   current->journal_info corruption).

Am I missing something?

If this observation is correct, the possible solution is to call
get_user_pages() or somehow pin the user pages before prepare_write(),
although it will hurt performance...

	Andrey
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