The patch titled
Subject: mm/hmm: potential deadlock in nonblocking code
has been added to the -mm tree. Its filename is
mm-hmm-improve-driver-api-to-work-and-wait-over-a-range-fix.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-hmm-improve-driver-api-to-work-and-wait-over-a-range-fix.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-hmm-improve-driver-api-to-work-and-wait-over-a-range-fix.patch
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------------------------------------------------------
From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Subject: mm/hmm: potential deadlock in nonblocking code
There is a deadlock bug when these functions are used in nonblocking mode.
The else side of the if/else statement is only meant to be taken in when
the code is used in blocking mode. But, unfortunately, the way the code
is now, if we're in non-blocking mode and we succeed in taking the lock
then we do the else statement. The else side tries to take lock a second
time which results in a deadlock.
Link: http://lkml.kernel.org/r/20190204182304.GA8756@kadam
Fixes: a3402cb621c1 ("mm/hmm: improve driver API to work and wait over a range")
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/mm/hmm.c~mm-hmm-improve-driver-api-to-work-and-wait-over-a-range-fix
+++ a/mm/hmm.c
@@ -206,11 +206,12 @@ static int hmm_invalidate_range_start(st
update.event = HMM_UPDATE_INVALIDATE;
update.blockable = nrange->blockable;
- if (!nrange->blockable && !mutex_trylock(&hmm->lock)) {
+ if (nrange->blockable)
+ mutex_lock(&hmm->lock);
+ else if (!mutex_trylock(&hmm->lock)) {
ret = -EAGAIN;
goto out;
- } else
- mutex_lock(&hmm->lock);
+ }
hmm->notifiers++;
list_for_each_entry(range, &hmm->ranges, list) {
if (update.end < range->start || update.start >= range->end)
@@ -220,12 +221,12 @@ static int hmm_invalidate_range_start(st
}
mutex_unlock(&hmm->lock);
-
- if (!nrange->blockable && !down_read_trylock(&hmm->mirrors_sem)) {
+ if (nrange->blockable)
+ down_read(&hmm->mirrors_sem);
+ else if (!down_read_trylock(&hmm->mirrors_sem)) {
ret = -EAGAIN;
goto out;
- } else
- down_read(&hmm->mirrors_sem);
+ }
list_for_each_entry(mirror, &hmm->mirrors, list) {
int ret;
_
Patches currently in -mm which might be from dan.carpenter@xxxxxxxxxx are
mm-hmm-improve-driver-api-to-work-and-wait-over-a-range-fix.patch
rapidio-potential-oops-in-riocm_ch_listen.patch
