tree 0a678f275a0d92d453b214abe9e8f2aba13d4c06
parent 2dfa67a1a4c049fd33fcc6abcb1c8ca57b17a268
author Dmitry Kasatkin <d.kasatkin@samsung.com> 1394009733 +0200
committer Dmitry Kasatkin <d.kasatkin@samsung.com> 1394009733 +0200

dm-integrity: avoid deadlock

Based on the patch: dm verity: avoid deadlock

A deadlock was found in the prefetch code in the dm verity map
function.  This patch fixes this by transferring the prefetch
to a worker thread and skipping it completely if kmalloc fails.

If generic_make_request is called recursively, it queues the I/O
request on the current->bio_list without making the I/O request
and returns. The routine making the recursive call cannot wait
for the I/O to complete.

The deadlock occurs when one thread grabs the bufio_client
mutex and waits for an I/O to complete but the I/O is queued
on another thread's current->bio_list and is waiting to get
the mutex held by the first thread.

The fix recognises that prefetching is not essential.  If memory
can be allocated, it queues the prefetch request to the worker thread,
but if not, it does nothing.

Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>