Re: [PATCH v3] btrfs: interrupt fstrim if the current process is freezing

[David Sterba <dsterba@suse.cz>]

On Fri, Aug 30, 2024 at 08:09:11AM +0930, Qu Wenruo wrote:
> [BUG]
> There is a bug report that running fstrim will prevent the system from
> hibernation, result the following dmesg:
> 
>  PM: suspend entry (deep)
>  Filesystems sync: 0.060 seconds
>  Freezing user space processes
>  Freezing user space processes failed after 20.007 seconds (1 tasks refusing to freeze, wq_busy=0):
>  task:fstrim          state:D stack:0     pid:15564 tgid:15564 ppid:1      flags:0x00004006
>  Call Trace:
>   <TASK>
>   __schedule+0x381/0x1540
>   schedule+0x24/0xb0
>   schedule_timeout+0x1ea/0x2a0
>   io_schedule_timeout+0x19/0x50
>   wait_for_completion_io+0x78/0x140
>   submit_bio_wait+0xaa/0xc0
>   blkdev_issue_discard+0x65/0xb0
>   btrfs_issue_discard+0xcf/0x160 [btrfs 7ab35b9b86062a46f6ff578bb32d55ecf8e6bf82]
>   btrfs_discard_extent+0x120/0x2a0 [btrfs 7ab35b9b86062a46f6ff578bb32d55ecf8e6bf82]
>   do_trimming+0xd4/0x220 [btrfs 7ab35b9b86062a46f6ff578bb32d55ecf8e6bf82]
>   trim_bitmaps+0x418/0x520 [btrfs 7ab35b9b86062a46f6ff578bb32d55ecf8e6bf82]
>   btrfs_trim_block_group+0xcb/0x130 [btrfs 7ab35b9b86062a46f6ff578bb32d55ecf8e6bf82]
>   btrfs_trim_fs+0x119/0x460 [btrfs 7ab35b9b86062a46f6ff578bb32d55ecf8e6bf82]
>   btrfs_ioctl_fitrim+0xfb/0x160 [btrfs 7ab35b9b86062a46f6ff578bb32d55ecf8e6bf82]
>   btrfs_ioctl+0x11cc/0x29f0 [btrfs 7ab35b9b86062a46f6ff578bb32d55ecf8e6bf82]
>   __x64_sys_ioctl+0x92/0xd0
>   do_syscall_64+0x5b/0x80
>   entry_SYSCALL_64_after_hwframe+0x7c/0xe6
>  RIP: 0033:0x7f5f3b529f9b
>  RSP: 002b:00007fff279ebc20 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>  RAX: ffffffffffffffda RBX: 00007fff279ebd60 RCX: 00007f5f3b529f9b
>  RDX: 00007fff279ebc90 RSI: 00000000c0185879 RDI: 0000000000000003
>  RBP: 000055748718b2d0 R08: 00005574871899e8 R09: 00007fff279eb010
>  R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
>  R13: 000055748718ac40 R14: 000055748718b290 R15: 000055748718b290
>   </TASK>
>  OOM killer enabled.
>  Restarting tasks ... done.
>  random: crng reseeded on system resumption
>  PM: suspend exit
>  PM: suspend entry (s2idle)
>  Filesystems sync: 0.047 seconds
> 
> [CAUSE]
> PM code is freezing all user space processes before entering
> hibernation/suspension, but if a user space process is trapping into the
> kernel for a long running operation, it will not be frozen since it's
> still inside kernel.
> 
> Normally those long running operations check for fatal signals and exit
> early, but freezing user space processes is not done by signals but a
> different infrastructure.
> 
> Unfortunately btrfs only checks fatal signals but not if the current
> task is being frozen for fstrim.
> 
> [FIX]
> For now just do the extra freezing() check at a per-block-group basis.
> 
> Reported-by: Rolf Wentland <R.Wentland@gmx.de>
> Link: https://bugzilla.suse.com/show_bug.cgi?id=1229737
> Signed-off-by: Qu Wenruo <wqu@suse.com>

As a quick fix it's ok, I hope there's some way to support freezing of
the ioctls, try_to_freeze() or schedule() at the right time could work.

Reviewed-by: David Sterba <dsterba@suse.com>