Contention on the dentry cache lock when umounting NFS volumes on Red Hat Enterprise Linux 5
Issue
Lock contention on the dcache_lock causes I/O problems host, with soft lockup warnings similar to:
BUG: soft lockup - CPU#10 stuck for 10s! [M1IF:3779]
Call Trace:
[<ffffffff8000c31a>] _atomic_dec_and_lock+0x39/0x57
[<ffffffff8000d052>] dput+0x2c/0x114
[<ffffffff80022b12>] path_release+0xc/0x24
[<ffffffff800285ff>] vfs_stat_fd+0x3c/0x4a
[<ffffffff8003aa41>] hrtimer_try_to_cancel+0x4a/0x53
[<ffffffff8005a21d>] hrtimer_cancel+0xc/0x16
[<ffffffff80063c5d>] do_nanosleep+0x47/0x70
[<ffffffff8005a10a>] hrtimer_nanosleep+0x58/0x118
[<ffffffff800233f9>] sys_newstat+0x19/0x31
[<ffffffff8005d28d>] tracesys+0xd5/0xe0
The dcache_lock protects modification of the in kernel dentry cache. A dentry is an in memory data structure describing a directory entry on disk.
Environment
- Red Hat Enterprise Linux 5, minor version 4 and earlier
kernel-2.6.18earlier thankernel-2.6.18-194
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