linux-kernel - Re: [PATCH v4 2/2] x86/mce/amd: Fix memory leak when `threshold_create

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Date:   Thu,  3 Mar 2022 01:58:26 +0000
From:   Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>,
        Yazen Ghannam <yazen.ghannam@....com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org, gwml@...r.gnuweeb.org,
        x86@...nel.org, stable@...r.kernel.org,
        Alviro Iskandar Setiawan <alviro.iskandar@...il.com>,
        Jiri Hladky <hladky.jiri@...glemail.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v4 2/2] x86/mce/amd: Fix memory leak when `threshold_create_bank()` fails

On Thu, 3 Mar 2022 06:27:33 +0700, Ammar Faizi wrote:
> +static void _mce_threshold_remove_device(struct threshold_bank **bp)
> +{
> +	unsigned int bank, numbanks = this_cpu_read(mce_num_banks);
> +
> +	for (bank = 0; bank < numbanks; bank++) {
> +		if (bp[bank]) {
> +			threshold_remove_bank(bp[bank]);
> +			bp[bank] = NULL;
> +		}
> +	}
> +	kfree(bp);
> +}

hi sir, i think this can be improved again, we can avoid calling
this_cpu_read(mce_num_banks) twice if we pass the numbanks as an
argument, plz review the changes below

diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
index 9f4b508886dd..e492efab68a2 100644
--- a/arch/x86/kernel/cpu/mce/amd.c
+++ b/arch/x86/kernel/cpu/mce/amd.c
@@ -1293,10 +1293,23 @@ static void threshold_remove_bank(struct threshold_bank *bank)
 	kfree(bank);
 }
 
+static void _mce_threshold_remove_device(struct threshold_bank **bp,
+					 unsigned int numbanks)
+{
+	unsigned int bank;
+
+	for (bank = 0; bank < numbanks; bank++) {
+		if (bp[bank]) {
+			threshold_remove_bank(bp[bank]);
+			bp[bank] = NULL;
+		}
+	}
+	kfree(bp);
+}
+
 int mce_threshold_remove_device(unsigned int cpu)
 {
 	struct threshold_bank **bp = this_cpu_read(threshold_banks);
-	unsigned int bank, numbanks = this_cpu_read(mce_num_banks);
 
 	if (!bp)
 		return 0;
@@ -1307,13 +1320,7 @@ int mce_threshold_remove_device(unsigned int cpu)
 	 */
 	this_cpu_write(threshold_banks, NULL);
 
-	for (bank = 0; bank < numbanks; bank++) {
-		if (bp[bank]) {
-			threshold_remove_bank(bp[bank]);
-			bp[bank] = NULL;
-		}
-	}
-	kfree(bp);
+	_mce_threshold_remove_device(bp, this_cpu_read(mce_num_banks));
 	return 0;
 }
 
@@ -1350,15 +1357,14 @@ int mce_threshold_create_device(unsigned int cpu)
 		if (!(this_cpu_read(bank_map) & (1 << bank)))
 			continue;
 		err = threshold_create_bank(bp, cpu, bank);
-		if (err)
-			goto out_err;
+		if (err) {
+			_mce_threshold_remove_device(bp, numbanks);
+			return err;
+		}
 	}
 	this_cpu_write(threshold_banks, bp);
 
 	if (thresholding_irq_en)
 		mce_threshold_vector = amd_threshold_interrupt;
 	return 0;
-out_err:
-	mce_threshold_remove_device(cpu);
-	return err;
 }

-- Viro