On Thu, 20 Jun 2024 14:43:50 +0200 Mateusz Kusiak <mateusz.kusiak@xxxxxxxxxxxxxxx> wrote: > On 18.06.2024 16:24, Mateusz Kusiak wrote: > > Hi all, > > we have an issue submitted for SLES15SP6 that is caused by huge delays when > > trying to remove drive from a container. > > > > The scenario is as follows: > > 1. Create two drive imsm container > > # mdadm --create --run /dev/md/imsm --metadata=imsm --raid-devices=2 > > /dev/nvme[0-1]n1 2. Remove single drive from container > > # mdadm /dev/md127 --remove /dev/nvme0n1 > > > > The problem is that drive removal may take up to 7 seconds, which causes > > timeouts for other components that are mdadm dependent. > > > > We narrowed it down to be MD related. We tested this with inbox mdadm-4.3 > > and mdadm-4.2 on SP6 and delay time is pretty much the same. SP5 is free of > > this issue. > > > > I also tried RHEL 8.9 and drive removal is almost instant. > > > > Is it default behavior now, or should we treat this as an issue? > > > > Thanks, > > Mateusz > > > > I dug into this more. I retested this on: > - Ubuntu 24.04 with inbox kernel 6.6.0: No reproduction > - RHEL 9.4 with usptream kernel: 6.9.5-1: Got reproduction > (Note that SLES15SP6 comes with 6.8.0-rc4 inbox) > > I plugged into mdadm with gdb and found out that ioctl call in > hot_remove_disk() fails and it's causing a delay. The function looks as > follows: > > int hot_remove_disk(int mdfd, unsigned long dev, int force) > { > int cnt = force ? 500 : 5; > int ret; > > /* HOT_REMOVE_DISK can fail with EBUSY if there are > * outstanding IO requests to the device. > * In this case, it can be helpful to wait a little while, > * up to 5 seconds if 'force' is set, or 50 msec if not. > */ > while ((ret = ioctl(mdfd, HOT_REMOVE_DISK, dev)) == -1 && > errno == EBUSY && > cnt-- > 0) > sleep_for(0, MSEC_TO_NSEC(10), true); > > return ret; > } > ... if it fails, then it defaults to removing drive via sysfs call. > > Looks like a kernel ioctl issue... > Hello, I investigated this. Looks like HOT_REMOVE_DRIVE ioctl almost always failed for raid with no raid personality. At some point it was allowed but it was blocked 6 years ago in c42a0e2675 (this id leads to merge commit, so giving title "md: fix NULL dereference of mddev->pers in remove_and_add_spares()"). And that explains why we have outdated comment in mdadm: if (err && errno == ENODEV) { /* Old kernels rejected this if no personality * is registered */ I'm working to make it fixed in mdadm (for kernels with this hang), I will remove ioctl call for external containers: https://github.com/md-raid-utilities/mdadm/pull/31 On HOT_REMOVE_DRIVE ioctl path, there is a wait for clearing MD_RECOVERY_NEEDED flag with timeout set to 5 seconds. When I disabled this for arrays with no personality- it fixes issue. However, I'm not sure if it is right fix. I would expect to not set MD_RECOVERY_NEEDED for arrays with no MD personality. Kuai and Song could you please advice? diff --git a/drivers/md/md.c b/drivers/md/md.c index c0426a6d2fd1..bd1cedeb105b 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -7827,7 +7827,7 @@ static int md_ioctl(struct block_device *bdev, blk_mode_t mode, return get_bitmap_file(mddev, argp); } - if (cmd == HOT_REMOVE_DISK) + if (cmd == HOT_REMOVE_DISK && mddev->pers) /* need to ensure recovery thread has run */ wait_event_interruptible_timeout(mddev->sb_wait, !test_bit(MD_RECOVERY_NEEDED, Thanks, Mariusz