diff options
| author | Jiri Bohac <jbohac@suse.cz> | 2025-06-12 12:18:40 +0200 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-07-19 19:08:23 -0700 |
| commit | e1280f3071f11abc1bacd84937ecf077dce449f3 (patch) | |
| tree | 9b3487993e3b7b56c4e09a08ecca62685f37f000 /kernel/crash_core.c | |
| parent | ce1bf19a34dfa1f418037cebe11f5d2c7adf9d1e (diff) | |
kdump: wait for DMA to finish when using CMA
When re-using the CMA area for kdump there is a risk of pending DMA into
pinned user pages in the CMA area.
Pages residing in CMA areas can usually not get long-term pinned and are
instead migrated away from the CMA area, so long-term pinning is typically
not a concern. (BUGs in the kernel might still lead to long-term pinning
of such pages if everything goes wrong.)
Pages pinned without FOLL_LONGTERM remain in the CMA and may possibly be
the source or destination of a pending DMA transfer.
Although there is no clear specification how long a page may be pinned
without FOLL_LONGTERM, pinning without the flag shows an intent of the
caller to only use the memory for short-lived DMA transfers, not a
transfer initiated by a device asynchronously at a random time in the
future.
Add a delay of CMA_DMA_TIMEOUT_SEC seconds before starting the kdump
kernel, giving such short-lived DMA transfers time to finish before the
CMA memory is re-used by the kdump kernel.
Set CMA_DMA_TIMEOUT_SEC to 10 seconds - chosen arbitrarily as both a huge
margin for a DMA transfer, yet not increasing the kdump time too
significantly.
Link: https://lkml.kernel.org/r/aEqpgDIBndZ5LXSo@dwarf.suse.cz
Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Donald Dutile <ddutile@redhat.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Philipp Rudo <prudo@redhat.com>
Cc: Pingfan Liu <piliu@redhat.com>
Cc: Tao Liu <ltao@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'kernel/crash_core.c')
| -rw-r--r-- | kernel/crash_core.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/kernel/crash_core.c b/kernel/crash_core.c index 335b8425dd4b..a4ef79591eb2 100644 --- a/kernel/crash_core.c +++ b/kernel/crash_core.c @@ -21,6 +21,7 @@ #include <linux/reboot.h> #include <linux/btf.h> #include <linux/objtool.h> +#include <linux/delay.h> #include <asm/page.h> #include <asm/sections.h> @@ -33,6 +34,11 @@ /* Per cpu memory for storing cpu states in case of system crash. */ note_buf_t __percpu *crash_notes; +/* time to wait for possible DMA to finish before starting the kdump kernel + * when a CMA reservation is used + */ +#define CMA_DMA_TIMEOUT_SEC 10 + #ifdef CONFIG_CRASH_DUMP int kimage_crash_copy_vmcoreinfo(struct kimage *image) @@ -97,6 +103,14 @@ int kexec_crash_loaded(void) } EXPORT_SYMBOL_GPL(kexec_crash_loaded); +static void crash_cma_clear_pending_dma(void) +{ + if (!crashk_cma_cnt) + return; + + mdelay(CMA_DMA_TIMEOUT_SEC * 1000); +} + /* * No panic_cpu check version of crash_kexec(). This function is called * only when panic_cpu holds the current CPU number; this is the only CPU @@ -119,6 +133,7 @@ void __noclone __crash_kexec(struct pt_regs *regs) crash_setup_regs(&fixed_regs, regs); crash_save_vmcoreinfo(); machine_crash_shutdown(&fixed_regs); + crash_cma_clear_pending_dma(); machine_kexec(kexec_crash_image); } kexec_unlock(); |