On 13/08/2020 03.45, Steven Rostedt wrote: > 5.4.54-rt33-rc1 stable review patch. > If anyone has any objections, please let me know. > No objections, quite the contrary. I think this should also be applied to 4.19-rt: Commit fda31c50292a is also in 4.19.y (as 797479da0ae9), since 4.19.112 and hence also 4.19.112-rt47. For a while we've tried to track down a hang that at least sometimes manifests quite similarly refcount_t: underflow; use-after-free. WARNING: CPU: 0 PID: 14 at lib/refcount.c:280 refcount_dec_not_one+0xc0/0xd8 ... Call Trace: [cf45be10] [c0238258] refcount_dec_not_one+0xc0/0xd8 (unreliable) [cf45be20] [c02383c8] refcount_dec_and_lock_irqsave+0x20/0xa4 [cf45be40] [c0024a70] free_uid+0x2c/0xa0 [cf45be60] [c00384f0] put_cred_rcu+0x58/0x8c [cf45be70] [c005f048] rcu_cpu_kthread+0x364/0x49c [cf45bee0] [c003a0d0] smpboot_thread_fn+0x21c/0x29c [cf45bf10] [c0036464] kthread+0xe0/0x10c [cf45bf40] [c000f1cc] ret_from_kernel_thread+0x14/0x1c But our reproducer is rather complicated and involves cutting power to neighbouring boards, and takes many minutes to trigger. So I tried Daniel's reproducer sigwaittest -t -a -p 98 and almost immediately got a trace much more similar to the one in the commit message refcount_t: underflow; use-after-free. WARNING: CPU: 0 PID: 1526 at lib/refcount.c:280 refcount_dec_not_one+0xc0/0xd8 ... Call Trace: [cebc9e00] [c0238258] refcount_dec_not_one+0xc0/0xd8 (unreliable) [cebc9e10] [c02383c8] refcount_dec_and_lock_irqsave+0x20/0xa4 [cebc9e30] [c0024a70] free_uid+0x2c/0xa0 [cebc9e50] [c002574c] dequeue_signal+0x90/0x1a4 [cebc9e80] [c0028f74] sys_rt_sigtimedwait+0x24c/0x288 [cebc9f40] [c000f12c] ret_from_syscall+0x0/0x40 With this patch applied, the sigwaittest has now run for 10 minutes without problems. I'll have to run some more tests with our reproducer to see if it really is the same issue, but even if not, the fact that the sigwaittest fails should be enough to put this in 4.19-rt. Three requests (in order of importance): * pull this into 4.19-rt * add a note about the sigwaittest reproducer to the commit log * do publish the rt-rcs in some git repository; that makes it a lot easier to cherry-pick and test patches Thanks, Rasmus
