Fix possible splice() mmap_sem deadlock
Nick Piggin points out that splice isn't being good about the mmap semaphore: while two readers can nest inside each others, it does leave a possible deadlock if a writer (ie a new mmap()) comes in during that nesting. Original "just move the locking" patch by Nick, replaced by one by me based on an optimistic pagefault_disable(). And then Jens tested and updated that patch. Reported-by: NNick Piggin <npiggin@suse.de> Tested-by: NJens Axboe <jens.axboe@oracle.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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