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authorDavidlohr Bueso <dave@stgolabs.net>2016-04-17 23:31:41 -0700
committerIngo Molnar <mingo@kernel.org>2016-04-19 10:49:19 +0200
commit6687659568e2ec5b3ac24b39c5d26ce8b9d90434 (patch)
treee8a09031737ca3499941a9df9205a6578d5706df /kernel/locking
parentc3b46c73264b03000d1e18b22f5caf63332547c9 (diff)
locking/pvqspinlock: Fix division by zero in qstat_read()
While playing with the qstat statistics (in <debugfs>/qlockstat/) I ran into the following splat on a VM when opening pv_hash_hops: divide error: 0000 [#1] SMP ... RIP: 0010:[<ffffffff810b61fe>] [<ffffffff810b61fe>] qstat_read+0x12e/0x1e0 ... Call Trace: [<ffffffff811cad7c>] ? mem_cgroup_commit_charge+0x6c/0xd0 [<ffffffff8119750c>] ? page_add_new_anon_rmap+0x8c/0xd0 [<ffffffff8118d3b9>] ? handle_mm_fault+0x1439/0x1b40 [<ffffffff811937a9>] ? do_mmap+0x449/0x550 [<ffffffff811d3de3>] ? __vfs_read+0x23/0xd0 [<ffffffff811d4ab2>] ? rw_verify_area+0x52/0xd0 [<ffffffff811d4bb1>] ? vfs_read+0x81/0x120 [<ffffffff811d5f12>] ? SyS_read+0x42/0xa0 [<ffffffff815720f6>] ? 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 <dbueso@suse.de> Reviewed-by: Waiman Long <Waiman.Long@hpe.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> 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 <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/qspinlock_stat.h8
1 files 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