Apologies for the previous HTML email, my bad.
Yes, it does make sense for inclusion in 4.9.
I went and tested 4.9, saw the same hang, and backported the relevant patches. 4.9 requires only 3 of the 5 needed for 4.4.
I sent the patchset to the list, you should see them soon.
Let me know if there's anything else you need.
Thanks, Matthew
On 11/04/19 4:44 AM, Sasha Levin wrote:
On Wed, Apr 10, 2019 at 04:54:51PM +1200, Matthew Ruffell wrote:
BugLink: https://bugs.launchpad.net/bugs/1775165
[Note to upstream] I understand that this patch is a little long for -stable, but this patch series fixes a real issue, seen by real users, is testable, and is made up from upstream commits. Please consider it.
[Impact]
When userspace tasks which are processing fanotify permission events act incorrectly, the fsnotify_mark_srcu SRCU is held indefinitely which causes the whole notification subsystem to hang.
This has been seen in production, and it can also be seen when running the Linux Test Project testsuite, specifically fanotify07.
[Fix]
Instead of holding the SRCU lock while waiting for userspace to respond, which may never happen, or not in the order we are expecting, we drop the fsnotify_mark_srcu SRCU lock before waiting for userspace response, and then reacquire the lock again when userspace responds.
The fixes are from a series of upstream commits:
05f0e38724e8449184acd8fbf0473ee5a07adc6c (cherry-pick) 9385a84d7e1f658bb2d96ab798393e4b16268aaa (backport) abc77577a669f424c5d0c185b9994f2621c52aa4 (backport)
The following are upstream commits necessary for the fixes to function:
35e481761cdc688dbee0ef552a13f49af8eba6cc (backport) 0918f1c309b86301605650c836ddd2021d311ae2 (cherry-pick)
This would also make sense for 4.9, right? I don't want to fix 4.4 without fixing 4.9 as well.
-- Thanks, Sasha