Sometimes the readout of /sys/kernel/debug/swiotlb/io_tlb_used and io_tlb_used_hiwater can be a huge number (e.g. 18446744073709551615), which is actually a negative number if we use "%ld" to print the number.
When swiotlb_create_default_debugfs() is running from late_initcall, mem->total_used may already be non-zero, because the storage driver may have already started to perform I/O operations: if the storage driver is built-in, its probe() callback is called before late_initcall.
swiotlb_create_debugfs_files() should not blindly set mem->total_used and mem->used_hiwater to 0; actually it doesn't have to initialize the fields at all, because the fields, as part of the global struct io_tlb_default_mem, have been implicitly initialized to zero.
Also don't explicitly set mem->transient_nslabs to 0.
Fixes: 8b0977ecc8b3 ("swiotlb: track and report io_tlb_used high water marks in debugfs") Fixes: 02e765697038 ("swiotlb: add debugfs to track swiotlb transient pool usage") Cc: stable@vger.kernel.org Signed-off-by: Dexuan Cui decui@microsoft.com --- kernel/dma/swiotlb.c | 4 ---- 1 file changed, 4 deletions(-)
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 86fe172b5958..4a9f02c13da6 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -1647,9 +1647,6 @@ DEFINE_DEBUGFS_ATTRIBUTE(fops_io_tlb_hiwater, io_tlb_hiwater_get, static void swiotlb_create_debugfs_files(struct io_tlb_mem *mem, const char *dirname) { - atomic_long_set(&mem->total_used, 0); - atomic_long_set(&mem->used_hiwater, 0); - mem->debugfs = debugfs_create_dir(dirname, io_tlb_default_mem.debugfs); if (!mem->nslabs) return; @@ -1660,7 +1657,6 @@ static void swiotlb_create_debugfs_files(struct io_tlb_mem *mem, debugfs_create_file("io_tlb_used_hiwater", 0600, mem->debugfs, mem, &fops_io_tlb_hiwater); #ifdef CONFIG_SWIOTLB_DYNAMIC - atomic_long_set(&mem->transient_nslabs, 0); debugfs_create_file("io_tlb_transient_nslabs", 0400, mem->debugfs, mem, &fops_io_tlb_transient_used); #endif
On 3/29/2024 12:28 PM, Dexuan Cui wrote:
Sometimes the readout of /sys/kernel/debug/swiotlb/io_tlb_used and io_tlb_used_hiwater can be a huge number (e.g. 18446744073709551615), which is actually a negative number if we use "%ld" to print the number.
When swiotlb_create_default_debugfs() is running from late_initcall, mem->total_used may already be non-zero, because the storage driver may have already started to perform I/O operations: if the storage driver is built-in, its probe() callback is called before late_initcall.
swiotlb_create_debugfs_files() should not blindly set mem->total_used and mem->used_hiwater to 0; actually it doesn't have to initialize the fields at all, because the fields, as part of the global struct io_tlb_default_mem, have been implicitly initialized to zero.
Also don't explicitly set mem->transient_nslabs to 0.
Fixes: 8b0977ecc8b3 ("swiotlb: track and report io_tlb_used high water marks in debugfs") Fixes: 02e765697038 ("swiotlb: add debugfs to track swiotlb transient pool usage") Cc: stable@vger.kernel.org Signed-off-by: Dexuan Cui decui@microsoft.com
kernel/dma/swiotlb.c | 4 ---- 1 file changed, 4 deletions(-)
Sorry, I'm missing a why in this commit message. Can you say what happens if the total_used and used_hiwater IS blindly set to 0? Is the only effect the change in the readout of the swiotlb debugfs files?
Thanks, Easwar
From: Easwar Hariharan eahariha@linux.microsoft.com Sent: Friday, March 29, 2024 12:47 PM [...] Sorry, I'm missing a why in this commit message. Can you say what happens if the total_used and used_hiwater IS blindly set to 0? Is the only effect the change in the readout of the swiotlb debugfs files?
Thanks, Easwar
Right, when the system is not doing any I/O, the readout may return a huge number while it should return 0. This is the only effect.
Thanks, Dexuan
From: Dexuan Cui Sent: Friday, March 29, 2024 1:23 PM To: Easwar Hariharan eahariha@linux.microsoft.com; hch@lst.de; m.szyprowski@samsung.com; robin.murphy@arm.com; zhangpeng362@huawei.com; iommu@lists.linux.dev; mhklinux@outlook.com Cc: linux-kernel@vger.kernel.org; stable@vger.kernel.org Subject: RE: [PATCH] swiotlb: Do not set total_used to 0 in swiotlb_create_debugfs_files()
From: Easwar Hariharan eahariha@linux.microsoft.com Sent: Friday, March 29, 2024 12:47 PM [...] Sorry, I'm missing a why in this commit message. Can you say what
happens
if the total_used and used_hiwater IS blindly set to 0? Is the only effect the change in the readout of the swiotlb debugfs files?
Thanks, Easwar
Right, when the system is not doing any I/O, the readout may return a huge number while it should return 0. This is the only effect.
Thanks, Dexuan
Let me share more details.
kernel/dma/swiotlb.c uses inc_used_and_hiwater() and dec_used() to do the accounting.
The issue happens this way:
1. inc_used_and_hiwater() adds n to total_used. 2. swiotlb_create_debugfs_files() sets total_used to 0. 3. dec_used() decreases total_used by n, i.e. total_used incorrectly becomes a negative number -n, which is a huge number since mem_used() converts the 'long' to 'unsigned long'.
Thanks, Dexuan
On 3/29/2024 1:30 PM, Dexuan Cui wrote:
From: Dexuan Cui Sent: Friday, March 29, 2024 1:23 PM To: Easwar Hariharan eahariha@linux.microsoft.com; hch@lst.de; m.szyprowski@samsung.com; robin.murphy@arm.com; zhangpeng362@huawei.com; iommu@lists.linux.dev; mhklinux@outlook.com Cc: linux-kernel@vger.kernel.org; stable@vger.kernel.org Subject: RE: [PATCH] swiotlb: Do not set total_used to 0 in swiotlb_create_debugfs_files()
From: Easwar Hariharan eahariha@linux.microsoft.com Sent: Friday, March 29, 2024 12:47 PM [...] Sorry, I'm missing a why in this commit message. Can you say what
happens
if the total_used and used_hiwater IS blindly set to 0? Is the only effect the change in the readout of the swiotlb debugfs files?
Thanks, Easwar
Right, when the system is not doing any I/O, the readout may return a huge number while it should return 0. This is the only effect.
Thanks, Dexuan
Let me share more details.
kernel/dma/swiotlb.c uses inc_used_and_hiwater() and dec_used() to do the accounting.
The issue happens this way:
- inc_used_and_hiwater() adds n to total_used.
- swiotlb_create_debugfs_files() sets total_used to 0.
- dec_used() decreases total_used by n, i.e. total_used incorrectly
becomes a negative number -n, which is a huge number since mem_used() converts the 'long' to 'unsigned long'.
Thanks, Dexuan
Thanks for the detail. I only ask because the patch is marked for stable, and I was wondering if it meets the criteria. But, as you mentioned off list, two Fixes tags probably do meet the bar.
Thanks, Easwar
From: Dexuan Cui decui@microsoft.com Sent: Friday, March 29, 2024 12:28 PM
Sometimes the readout of /sys/kernel/debug/swiotlb/io_tlb_used and io_tlb_used_hiwater can be a huge number (e.g. 18446744073709551615), which is actually a negative number if we use "%ld" to print the number.
When swiotlb_create_default_debugfs() is running from late_initcall, mem->total_used may already be non-zero, because the storage driver may have already started to perform I/O operations: if the storage driver is built-in, its probe() callback is called before late_initcall.
swiotlb_create_debugfs_files() should not blindly set mem->total_used and mem->used_hiwater to 0; actually it doesn't have to initialize the fields at all, because the fields, as part of the global struct io_tlb_default_mem, have been implicitly initialized to zero.
Also don't explicitly set mem->transient_nslabs to 0.
Fixes: 8b0977ecc8b3 ("swiotlb: track and report io_tlb_used high water marks in debugfs") Fixes: 02e765697038 ("swiotlb: add debugfs to track swiotlb transient pool usage") Cc: stable@vger.kernel.org Signed-off-by: Dexuan Cui decui@microsoft.com
kernel/dma/swiotlb.c | 4 ---- 1 file changed, 4 deletions(-)
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 86fe172b5958..4a9f02c13da6 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -1647,9 +1647,6 @@ DEFINE_DEBUGFS_ATTRIBUTE(fops_io_tlb_hiwater, io_tlb_hiwater_get, static void swiotlb_create_debugfs_files(struct io_tlb_mem *mem, const char *dirname) {
- atomic_long_set(&mem->total_used, 0);
- atomic_long_set(&mem->used_hiwater, 0);
- mem->debugfs = debugfs_create_dir(dirname, io_tlb_default_mem.debugfs); if (!mem->nslabs) return;
@@ -1660,7 +1657,6 @@ static void swiotlb_create_debugfs_files(struct io_tlb_mem *mem, debugfs_create_file("io_tlb_used_hiwater", 0600, mem->debugfs, mem, &fops_io_tlb_hiwater); #ifdef CONFIG_SWIOTLB_DYNAMIC
- atomic_long_set(&mem->transient_nslabs, 0); debugfs_create_file("io_tlb_transient_nslabs", 0400, mem->debugfs, mem, &fops_io_tlb_transient_used);
#endif
2.34.1
Reviewed-by: Michael Kelley mhklinux@outlook.com
On 2024/3/30 3:28, Dexuan Cui wrote:
Sometimes the readout of /sys/kernel/debug/swiotlb/io_tlb_used and io_tlb_used_hiwater can be a huge number (e.g. 18446744073709551615), which is actually a negative number if we use "%ld" to print the number.
When swiotlb_create_default_debugfs() is running from late_initcall, mem->total_used may already be non-zero, because the storage driver may have already started to perform I/O operations: if the storage driver is built-in, its probe() callback is called before late_initcall.
swiotlb_create_debugfs_files() should not blindly set mem->total_used and mem->used_hiwater to 0; actually it doesn't have to initialize the fields at all, because the fields, as part of the global struct io_tlb_default_mem, have been implicitly initialized to zero.
Also don't explicitly set mem->transient_nslabs to 0.
Fixes: 8b0977ecc8b3 ("swiotlb: track and report io_tlb_used high water marks in debugfs") Fixes: 02e765697038 ("swiotlb: add debugfs to track swiotlb transient pool usage") Cc: stable@vger.kernel.org Signed-off-by: Dexuan Cui decui@microsoft.com
Reviewed-by: ZhangPengzhangpeng362@huawei.com
V Fri, 29 Mar 2024 12:28:09 -0700 Dexuan Cui decui@microsoft.com napsáno:
Sometimes the readout of /sys/kernel/debug/swiotlb/io_tlb_used and io_tlb_used_hiwater can be a huge number (e.g. 18446744073709551615), which is actually a negative number if we use "%ld" to print the number.
When swiotlb_create_default_debugfs() is running from late_initcall, mem->total_used may already be non-zero, because the storage driver may have already started to perform I/O operations: if the storage driver is built-in, its probe() callback is called before late_initcall.
swiotlb_create_debugfs_files() should not blindly set mem->total_used and mem->used_hiwater to 0; actually it doesn't have to initialize the fields at all, because the fields, as part of the global struct io_tlb_default_mem, have been implicitly initialized to zero.
Also don't explicitly set mem->transient_nslabs to 0.
Fixes: 8b0977ecc8b3 ("swiotlb: track and report io_tlb_used high water marks in debugfs") Fixes: 02e765697038 ("swiotlb: add debugfs to track swiotlb transient pool usage") Cc: stable@vger.kernel.org Signed-off-by: Dexuan Cui decui@microsoft.com
FWIW I confirm that the transient_nslabs counter does not have to be initialized either.
Reviewed-by: Petr Tesarik petr.tesarik1@huawei-partners.com
Petr T
linux-stable-mirror@lists.linaro.org
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Christoph Hellwig -
Dexuan Cui -
Easwar Hariharan -
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