The patch titled
Subject: mm: avoid overflows in dirty throttling logic
has been added to the -mm mm-unstable branch. Its filename is
mm-avoid-overflows-in-dirty-throttling-logic.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-avoid-overflows-in-dirty-throttling-logic.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: mm: avoid overflows in dirty throttling logic
Date: Fri, 21 Jun 2024 16:42:38 +0200
The dirty throttling logic is interspersed with assumptions that dirty
limits in PAGE_SIZE units fit into 32-bit (so that various multiplications
fit into 64-bits). If limits end up being larger, we will hit overflows,
possible divisions by 0 etc. Fix these problems by never allowing so
large dirty limits as they have dubious practical value anyway. For
dirty_bytes / dirty_background_bytes interfaces we can just refuse to set
so large limits. For dirty_ratio / dirty_background_ratio it isn't so
simple as the dirty limit is computed from the amount of available memory
which can change due to memory hotplug etc. So when converting dirty
limits from ratios to numbers of pages, we just don't allow the result to
exceed UINT_MAX.
Link: https://lkml.kernel.org/r/20240621144246.11148-2-jack@xxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
Reported-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 30 ++++++++++++++++++++++++++----
1 file changed, 26 insertions(+), 4 deletions(-)
--- a/mm/page-writeback.c~mm-avoid-overflows-in-dirty-throttling-logic
+++ a/mm/page-writeback.c
@@ -417,13 +417,20 @@ static void domain_dirty_limits(struct d
else
bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
- if (bg_thresh >= thresh)
- bg_thresh = thresh / 2;
tsk = current;
if (rt_task(tsk)) {
bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
}
+ /*
+ * Dirty throttling logic assumes the limits in page units fit into
+ * 32-bits. This gives 16TB dirty limits max which is hopefully enough.
+ */
+ if (thresh > UINT_MAX)
+ thresh = UINT_MAX;
+ /* This makes sure bg_thresh is within 32-bits as well */
+ if (bg_thresh >= thresh)
+ bg_thresh = thresh / 2;
dtc->thresh = thresh;
dtc->bg_thresh = bg_thresh;
@@ -473,7 +480,11 @@ static unsigned long node_dirty_limit(st
if (rt_task(tsk))
dirty += dirty / 4;
- return dirty;
+ /*
+ * Dirty throttling logic assumes the limits in page units fit into
+ * 32-bits. This gives 16TB dirty limits max which is hopefully enough.
+ */
+ return min_t(unsigned long, dirty, UINT_MAX);
}
/**
@@ -510,10 +521,17 @@ static int dirty_background_bytes_handle
void *buffer, size_t *lenp, loff_t *ppos)
{
int ret;
+ unsigned long old_bytes = dirty_background_bytes;
ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
- if (ret == 0 && write)
+ if (ret == 0 && write) {
+ if (DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE) >
+ UINT_MAX) {
+ dirty_background_bytes = old_bytes;
+ return -ERANGE;
+ }
dirty_background_ratio = 0;
+ }
return ret;
}
@@ -539,6 +557,10 @@ static int dirty_bytes_handler(struct ct
ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
+ if (DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) > UINT_MAX) {
+ vm_dirty_bytes = old_bytes;
+ return -ERANGE;
+ }
writeback_set_ratelimit();
vm_dirty_ratio = 0;
}
_
Patches currently in -mm which might be from jack@xxxxxxx are
ocfs2-fix-dio-failure-due-to-insufficient-transaction-credits.patch
revert-mm-writeback-fix-possible-divide-by-zero-in-wb_dirty_limits-again.patch
mm-avoid-overflows-in-dirty-throttling-logic.patch
