From 6687659568e2ec5b3ac24b39c5d26ce8b9d90434 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Sun, 17 Apr 2016 23:31:41 -0700 Subject: [PATCH] locking/pvqspinlock: Fix division by zero in qstat_read() While playing with the qstat statistics (in /qlockstat/) I ran into the following splat on a VM when opening pv_hash_hops: divide error: 0000 [#1] SMP ... RIP: 0010:[] [] qstat_read+0x12e/0x1e0 ... Call Trace: [] ? mem_cgroup_commit_charge+0x6c/0xd0 [] ? page_add_new_anon_rmap+0x8c/0xd0 [] ? handle_mm_fault+0x1439/0x1b40 [] ? do_mmap+0x449/0x550 [] ? __vfs_read+0x23/0xd0 [] ? rw_verify_area+0x52/0xd0 [] ? vfs_read+0x81/0x120 [] ? SyS_read+0x42/0xa0 [] ? entry_SYSCALL_64_fastpath+0x1e/0xa8 Fix this by verifying that qstat_pv_kick_unlock is in fact non-zero, similarly to what the qstat_pv_latency_wake case does, as if nothing else, this can come from resetting the statistics, thus having 0 kicks should be quite valid in this context. Signed-off-by: Davidlohr Bueso Reviewed-by: Waiman Long Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dave@stgolabs.net Cc: waiman.long@hpe.com Link: http://lkml.kernel.org/r/1460961103-24953-1-git-send-email-dave@stgolabs.net Signed-off-by: Ingo Molnar --- kernel/locking/qspinlock_stat.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h index eb2a2c9bc3fc..d734b7502001 100644 --- a/kernel/locking/qspinlock_stat.h +++ b/kernel/locking/qspinlock_stat.h @@ -136,10 +136,12 @@ static ssize_t qstat_read(struct file *file, char __user *user_buf, } if (counter == qstat_pv_hash_hops) { - u64 frac; + u64 frac = 0; - frac = 100ULL * do_div(stat, kicks); - frac = DIV_ROUND_CLOSEST_ULL(frac, kicks); + if (kicks) { + frac = 100ULL * do_div(stat, kicks); + frac = DIV_ROUND_CLOSEST_ULL(frac, kicks); + } /* * Return a X.XX decimal number