| Message ID | 20231226214610.109282-1-surenb@google.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 46e714c729c8d1d8110bc0545d7ffe8a759c9dc0 |
| Headers | show |
| Series | [1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock | expand |
Hello: This patch was applied to riscv/linux.git (fixes) by Andrew Morton <akpm@linux-foundation.org>: On Tue, 26 Dec 2023 13:46:10 -0800 you wrote: > A test [1] in Android test suite started failing after [2] was merged. > It turns out that after handling a major fault under per-VMA lock, the > process major fault counter does not register that fault as major. > Before [2] read faults would be done under mmap_lock, in which case > FAULT_FLAG_TRIED flag is set before retrying. That in turn causes > mm_account_fault() to account the fault as major once retry completes. > With per-VMA locks we often retry because a fault can't be handled > without locking the whole mm using mmap_lock. Therefore such retries > do not set FAULT_FLAG_TRIED flag. This logic does not work after [2] > because we can now handle read major faults under per-VMA lock and > upon retry the fact there was a major fault gets lost. Fix this by > setting FAULT_FLAG_TRIED after retrying under per-VMA lock if > VM_FAULT_MAJOR was returned. Ideally we would use an additional > VM_FAULT bit to indicate the reason for the retry (could not handle > under per-VMA lock vs other reason) but this simpler solution seems > to work, so keeping it simple. > > [...] Here is the summary with links: - [1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock https://git.kernel.org/riscv/c/46e714c729c8 You are awesome, thank you!
On Sat, Jan 20, 2024 at 09:09:47PM +0000, patchwork-bot+linux-riscv@kernel.org wrote: > Hello: > > This patch was applied to riscv/linux.git (fixes) > by Andrew Morton <akpm@linux-foundation.org>: > > On Tue, 26 Dec 2023 13:46:10 -0800 you wrote: > > A test [1] in Android test suite started failing after [2] was merged. > > It turns out that after handling a major fault under per-VMA lock, the > > process major fault counter does not register that fault as major. > > Before [2] read faults would be done under mmap_lock, in which case > > FAULT_FLAG_TRIED flag is set before retrying. That in turn causes > > mm_account_fault() to account the fault as major once retry completes. > > With per-VMA locks we often retry because a fault can't be handled > > without locking the whole mm using mmap_lock. Therefore such retries > > do not set FAULT_FLAG_TRIED flag. This logic does not work after [2] > > because we can now handle read major faults under per-VMA lock and > > upon retry the fact there was a major fault gets lost. Fix this by > > setting FAULT_FLAG_TRIED after retrying under per-VMA lock if > > VM_FAULT_MAJOR was returned. Ideally we would use an additional > > VM_FAULT bit to indicate the reason for the retry (could not handle > > under per-VMA lock vs other reason) but this simpler solution seems > > to work, so keeping it simple. > > > > [...] > > Here is the summary with links: > - [1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock > https://git.kernel.org/riscv/c/46e714c729c8 > > You are awesome, thank you! Now that 32-bit ARM has support for the per-VMA lock, does that also need to be patched?
On Sat, Jan 20, 2024 at 1:15 PM Russell King (Oracle) <linux@armlinux.org.uk> wrote: > > On Sat, Jan 20, 2024 at 09:09:47PM +0000, patchwork-bot+linux-riscv@kernel.org wrote: > > Hello: > > > > This patch was applied to riscv/linux.git (fixes) > > by Andrew Morton <akpm@linux-foundation.org>: > > > > On Tue, 26 Dec 2023 13:46:10 -0800 you wrote: > > > A test [1] in Android test suite started failing after [2] was merged. > > > It turns out that after handling a major fault under per-VMA lock, the > > > process major fault counter does not register that fault as major. > > > Before [2] read faults would be done under mmap_lock, in which case > > > FAULT_FLAG_TRIED flag is set before retrying. That in turn causes > > > mm_account_fault() to account the fault as major once retry completes. > > > With per-VMA locks we often retry because a fault can't be handled > > > without locking the whole mm using mmap_lock. Therefore such retries > > > do not set FAULT_FLAG_TRIED flag. This logic does not work after [2] > > > because we can now handle read major faults under per-VMA lock and > > > upon retry the fact there was a major fault gets lost. Fix this by > > > setting FAULT_FLAG_TRIED after retrying under per-VMA lock if > > > VM_FAULT_MAJOR was returned. Ideally we would use an additional > > > VM_FAULT bit to indicate the reason for the retry (could not handle > > > under per-VMA lock vs other reason) but this simpler solution seems > > > to work, so keeping it simple. > > > > > > [...] > > > > Here is the summary with links: > > - [1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock > > https://git.kernel.org/riscv/c/46e714c729c8 > > > > You are awesome, thank you! > > Now that 32-bit ARM has support for the per-VMA lock, does that also > need to be patched? Yes, I think so. I missed the ARM32 change that added support for per-VMA locks. Will post a similar patch for it tomorrow. Thanks, Suren. > > -- > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
On Sun, Jan 21, 2024 at 11:38 PM Suren Baghdasaryan <surenb@google.com> wrote: > > On Sat, Jan 20, 2024 at 1:15 PM Russell King (Oracle) > <linux@armlinux.org.uk> wrote: > > > > On Sat, Jan 20, 2024 at 09:09:47PM +0000, patchwork-bot+linux-riscv@kernel.org wrote: > > > Hello: > > > > > > This patch was applied to riscv/linux.git (fixes) > > > by Andrew Morton <akpm@linux-foundation.org>: > > > > > > On Tue, 26 Dec 2023 13:46:10 -0800 you wrote: > > > > A test [1] in Android test suite started failing after [2] was merged. > > > > It turns out that after handling a major fault under per-VMA lock, the > > > > process major fault counter does not register that fault as major. > > > > Before [2] read faults would be done under mmap_lock, in which case > > > > FAULT_FLAG_TRIED flag is set before retrying. That in turn causes > > > > mm_account_fault() to account the fault as major once retry completes. > > > > With per-VMA locks we often retry because a fault can't be handled > > > > without locking the whole mm using mmap_lock. Therefore such retries > > > > do not set FAULT_FLAG_TRIED flag. This logic does not work after [2] > > > > because we can now handle read major faults under per-VMA lock and > > > > upon retry the fact there was a major fault gets lost. Fix this by > > > > setting FAULT_FLAG_TRIED after retrying under per-VMA lock if > > > > VM_FAULT_MAJOR was returned. Ideally we would use an additional > > > > VM_FAULT bit to indicate the reason for the retry (could not handle > > > > under per-VMA lock vs other reason) but this simpler solution seems > > > > to work, so keeping it simple. > > > > > > > > [...] > > > > > > Here is the summary with links: > > > - [1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock > > > https://git.kernel.org/riscv/c/46e714c729c8 > > > > > > You are awesome, thank you! > > > > Now that 32-bit ARM has support for the per-VMA lock, does that also > > need to be patched? > > Yes, I think so. I missed the ARM32 change that added support for > per-VMA locks. Will post a similar patch for it tomorrow. Fix for ARM posted at https://lore.kernel.org/all/20240123064305.2829244-1-surenb@google.com/ > Thanks, > Suren. > > > > > -- > > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > > FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 460d799e1296..55f6455a8284 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -607,6 +607,8 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, goto done; } count_vm_vma_lock_event(VMA_LOCK_RETRY); + if (fault & VM_FAULT_MAJOR) + mm_flags |= FAULT_FLAG_TRIED; /* Quick path to respond to signals */ if (fault_signal_pending(fault, regs)) { diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index 9e49ede2bc1c..53335ae21a40 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -497,6 +497,8 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address, goto done; } count_vm_vma_lock_event(VMA_LOCK_RETRY); + if (fault & VM_FAULT_MAJOR) + flags |= FAULT_FLAG_TRIED; if (fault_signal_pending(fault, regs)) return user_mode(regs) ? 0 : SIGBUS; diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c index 90d4ba36d1d0..081339ddf47e 100644 --- a/arch/riscv/mm/fault.c +++ b/arch/riscv/mm/fault.c @@ -304,6 +304,8 @@ void handle_page_fault(struct pt_regs *regs) goto done; } count_vm_vma_lock_event(VMA_LOCK_RETRY); + if (fault & VM_FAULT_MAJOR) + flags |= FAULT_FLAG_TRIED; if (fault_signal_pending(fault, regs)) { if (!user_mode(regs)) diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c index 249aefcf7c4e..ab4098886e56 100644 --- a/arch/s390/mm/fault.c +++ b/arch/s390/mm/fault.c @@ -337,6 +337,9 @@ static void do_exception(struct pt_regs *regs, int access) return; } count_vm_vma_lock_event(VMA_LOCK_RETRY); + if (fault & VM_FAULT_MAJOR) + flags |= FAULT_FLAG_TRIED; + /* Quick path to respond to signals */ if (fault_signal_pending(fault, regs)) { if (!user_mode(regs)) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index ab778eac1952..679b09cfe241 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1370,6 +1370,8 @@ void do_user_addr_fault(struct pt_regs *regs, goto done; } count_vm_vma_lock_event(VMA_LOCK_RETRY); + if (fault & VM_FAULT_MAJOR) + flags |= FAULT_FLAG_TRIED; /* Quick path to respond to signals */ if (fault_signal_pending(fault, regs)) {
A test [1] in Android test suite started failing after [2] was merged. It turns out that after handling a major fault under per-VMA lock, the process major fault counter does not register that fault as major. Before [2] read faults would be done under mmap_lock, in which case FAULT_FLAG_TRIED flag is set before retrying. That in turn causes mm_account_fault() to account the fault as major once retry completes. With per-VMA locks we often retry because a fault can't be handled without locking the whole mm using mmap_lock. Therefore such retries do not set FAULT_FLAG_TRIED flag. This logic does not work after [2] because we can now handle read major faults under per-VMA lock and upon retry the fact there was a major fault gets lost. Fix this by setting FAULT_FLAG_TRIED after retrying under per-VMA lock if VM_FAULT_MAJOR was returned. Ideally we would use an additional VM_FAULT bit to indicate the reason for the retry (could not handle under per-VMA lock vs other reason) but this simpler solution seems to work, so keeping it simple. [1] https://cs.android.com/android/platform/superproject/+/master:test/vts-testcase/kernel/api/drop_caches_prop/drop_caches_test.cpp [2] https://lore.kernel.org/all/20231006195318.4087158-6-willy@infradead.org/ Fixes: 12214eba1992 ("mm: handle read faults under the VMA lock") Cc: Matthew Wilcox <willy@infradead.org> Signed-off-by: Suren Baghdasaryan <surenb@google.com> --- arch/arm64/mm/fault.c | 2 ++ arch/powerpc/mm/fault.c | 2 ++ arch/riscv/mm/fault.c | 2 ++ arch/s390/mm/fault.c | 3 +++ arch/x86/mm/fault.c | 2 ++ 5 files changed, 11 insertions(+)