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authorPeter Xu2020-04-01 21:08:45 -0700
committerLinus Torvalds2020-04-02 09:35:30 -0700
commit4064b982706375025628094e51d11cf1a958a5d3 (patch)
treedc88974da3795f26c8cf9b56740b9bd04f4a97e2 /arch
parentc270a7eedcf278304e05ebd2c96807487c97db61 (diff)
mm: allow VM_FAULT_RETRY for multiple times
The idea comes from a discussion between Linus and Andrea [1]. Before this patch we only allow a page fault to retry once. We achieved this by clearing the FAULT_FLAG_ALLOW_RETRY flag when doing handle_mm_fault() the second time. This was majorly used to avoid unexpected starvation of the system by looping over forever to handle the page fault on a single page. However that should hardly happen, and after all for each code path to return a VM_FAULT_RETRY we'll first wait for a condition (during which time we should possibly yield the cpu) to happen before VM_FAULT_RETRY is really returned. This patch removes the restriction by keeping the FAULT_FLAG_ALLOW_RETRY flag when we receive VM_FAULT_RETRY. It means that the page fault handler now can retry the page fault for multiple times if necessary without the need to generate another page fault event. Meanwhile we still keep the FAULT_FLAG_TRIED flag so page fault handler can still identify whether a page fault is the first attempt or not. Then we'll have these combinations of fault flags (only considering ALLOW_RETRY flag and TRIED flag): - ALLOW_RETRY and !TRIED: this means the page fault allows to retry, and this is the first try - ALLOW_RETRY and TRIED: this means the page fault allows to retry, and this is not the first try - !ALLOW_RETRY and !TRIED: this means the page fault does not allow to retry at all - !ALLOW_RETRY and TRIED: this is forbidden and should never be used In existing code we have multiple places that has taken special care of the first condition above by checking against (fault_flags & FAULT_FLAG_ALLOW_RETRY). This patch introduces a simple helper to detect the first retry of a page fault by checking against both (fault_flags & FAULT_FLAG_ALLOW_RETRY) and !(fault_flag & FAULT_FLAG_TRIED) because now even the 2nd try will have the ALLOW_RETRY set, then use that helper in all existing special paths. One example is in __lock_page_or_retry(), now we'll drop the mmap_sem only in the first attempt of page fault and we'll keep it in follow up retries, so old locking behavior will be retained. This will be a nice enhancement for current code [2] at the same time a supporting material for the future userfaultfd-writeprotect work, since in that work there will always be an explicit userfault writeprotect retry for protected pages, and if that cannot resolve the page fault (e.g., when userfaultfd-writeprotect is used in conjunction with swapped pages) then we'll possibly need a 3rd retry of the page fault. It might also benefit other potential users who will have similar requirement like userfault write-protection. GUP code is not touched yet and will be covered in follow up patch. Please read the thread below for more information. [1] https://lore.kernel.org/lkml/20171102193644.GB22686@redhat.com/ [2] https://lore.kernel.org/lkml/20181230154648.GB9832@redhat.com/ Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Suggested-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Brian Geffon <bgeffon@google.com> Cc: Bobby Powers <bobbypowers@gmail.com> Cc: David Hildenbrand <david@redhat.com> Cc: Denis Plotnikov <dplotnikov@virtuozzo.com> Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Martin Cracauer <cracauer@cons.org> Cc: Marty McFadden <mcfadden8@llnl.gov> Cc: Matthew Wilcox <willy@infradead.org> Cc: Maya Gokhale <gokhale2@llnl.gov> Cc: Mel Gorman <mgorman@suse.de> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Pavel Emelyanov <xemul@openvz.org> Link: http://lkml.kernel.org/r/20200220160246.9790-1-peterx@redhat.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/alpha/mm/fault.c2
-rw-r--r--arch/arc/mm/fault.c1
-rw-r--r--arch/arm/mm/fault.c3
-rw-r--r--arch/arm64/mm/fault.c5
-rw-r--r--arch/hexagon/mm/vm_fault.c1
-rw-r--r--arch/ia64/mm/fault.c1
-rw-r--r--arch/m68k/mm/fault.c3
-rw-r--r--arch/microblaze/mm/fault.c1
-rw-r--r--arch/mips/mm/fault.c1
-rw-r--r--arch/nds32/mm/fault.c1
-rw-r--r--arch/nios2/mm/fault.c3
-rw-r--r--arch/openrisc/mm/fault.c1
-rw-r--r--arch/parisc/mm/fault.c4
-rw-r--r--arch/powerpc/mm/fault.c6
-rw-r--r--arch/riscv/mm/fault.c5
-rw-r--r--arch/s390/mm/fault.c5
-rw-r--r--arch/sh/mm/fault.c1
-rw-r--r--arch/sparc/mm/fault_32.c1
-rw-r--r--arch/sparc/mm/fault_64.c1
-rw-r--r--arch/um/kernel/trap.c1
-rw-r--r--arch/unicore32/mm/fault.c4
-rw-r--r--arch/x86/mm/fault.c2
-rw-r--r--arch/xtensa/mm/fault.c1
23 files changed, 4 insertions, 50 deletions
diff --git a/arch/alpha/mm/fault.c b/arch/alpha/mm/fault.c
index fcfa229cc1e7..c2d7b6d7bac7 100644
--- a/arch/alpha/mm/fault.c
+++ b/arch/alpha/mm/fault.c
@@ -169,7 +169,7 @@ retry:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
+ flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
* have already released it in __lock_page_or_retry
diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index 643fad774071..92b339c7adba 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -145,7 +145,6 @@ retry:
*/
if (unlikely((fault & VM_FAULT_RETRY) &&
(flags & FAULT_FLAG_ALLOW_RETRY))) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
}
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 18ef0b143ac2..b598e6978b29 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -319,9 +319,6 @@ retry:
regs, addr);
}
if (fault & VM_FAULT_RETRY) {
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
}
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index cbb29a43aa7f..1027851d469a 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -521,12 +521,7 @@ retry:
}
if (fault & VM_FAULT_RETRY) {
- /*
- * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk of
- * starvation.
- */
if (mm_flags & FAULT_FLAG_ALLOW_RETRY) {
- mm_flags &= ~FAULT_FLAG_ALLOW_RETRY;
mm_flags |= FAULT_FLAG_TRIED;
goto retry;
}
diff --git a/arch/hexagon/mm/vm_fault.c b/arch/hexagon/mm/vm_fault.c
index d9e15d941bdb..72334b26317a 100644
--- a/arch/hexagon/mm/vm_fault.c
+++ b/arch/hexagon/mm/vm_fault.c
@@ -102,7 +102,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
}
diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index b5aa4e80c762..30d0c1fca99e 100644
--- a/arch/ia64/mm/fault.c
+++ b/arch/ia64/mm/fault.c
@@ -167,7 +167,6 @@ retry:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
index 182799fd9987..f7afb9897966 100644
--- a/arch/m68k/mm/fault.c
+++ b/arch/m68k/mm/fault.c
@@ -162,9 +162,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
diff --git a/arch/microblaze/mm/fault.c b/arch/microblaze/mm/fault.c
index 32da02778a63..3248141f8ed5 100644
--- a/arch/microblaze/mm/fault.c
+++ b/arch/microblaze/mm/fault.c
@@ -236,7 +236,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c
index ec464da64656..4a0eafe3d932 100644
--- a/arch/mips/mm/fault.c
+++ b/arch/mips/mm/fault.c
@@ -178,7 +178,6 @@ good_area:
tsk->min_flt++;
}
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
diff --git a/arch/nds32/mm/fault.c b/arch/nds32/mm/fault.c
index 2810a4e5ab27..0cf0c08c7da2 100644
--- a/arch/nds32/mm/fault.c
+++ b/arch/nds32/mm/fault.c
@@ -246,7 +246,6 @@ good_area:
1, regs, addr);
}
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
diff --git a/arch/nios2/mm/fault.c b/arch/nios2/mm/fault.c
index c38bea4220fb..ec9d8a9c426f 100644
--- a/arch/nios2/mm/fault.c
+++ b/arch/nios2/mm/fault.c
@@ -157,9 +157,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
diff --git a/arch/openrisc/mm/fault.c b/arch/openrisc/mm/fault.c
index 30d5c51e9d40..8af1cc78c4fb 100644
--- a/arch/openrisc/mm/fault.c
+++ b/arch/openrisc/mm/fault.c
@@ -181,7 +181,6 @@ good_area:
else
tsk->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
index 8e88e5c5f26a..86e8c848f3d7 100644
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -328,14 +328,12 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
-
/*
* No need to up_read(&mm->mmap_sem) as we would
* have already released it in __lock_page_or_retry
* in mm/filemap.c.
*/
-
+ flags |= FAULT_FLAG_TRIED;
goto retry;
}
}
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index d7e1f8dc7e4c..d15f0f0ee806 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -590,13 +590,7 @@ good_area:
* case.
*/
if (unlikely(fault & VM_FAULT_RETRY)) {
- /* We retry only once */
if (flags & FAULT_FLAG_ALLOW_RETRY) {
- /*
- * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation.
- */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
}
diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index a252d9e38561..be84e32adc4c 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -144,11 +144,6 @@ good_area:
1, regs, addr);
}
if (fault & VM_FAULT_RETRY) {
- /*
- * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation.
- */
- flags &= ~(FAULT_FLAG_ALLOW_RETRY);
flags |= FAULT_FLAG_TRIED;
/*
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 551ac311bd35..aeccdb30899a 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -513,10 +513,7 @@ retry:
fault = VM_FAULT_PFAULT;
goto out_up;
}
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~(FAULT_FLAG_ALLOW_RETRY |
- FAULT_FLAG_RETRY_NOWAIT);
+ flags &= ~FAULT_FLAG_RETRY_NOWAIT;
flags |= FAULT_FLAG_TRIED;
down_read(&mm->mmap_sem);
goto retry;
diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c
index d9c8f2d00a54..13ee4d20e622 100644
--- a/arch/sh/mm/fault.c
+++ b/arch/sh/mm/fault.c
@@ -481,7 +481,6 @@ good_area:
regs, address);
}
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
diff --git a/arch/sparc/mm/fault_32.c b/arch/sparc/mm/fault_32.c
index a91b0c2d84f8..f6e0e601f857 100644
--- a/arch/sparc/mm/fault_32.c
+++ b/arch/sparc/mm/fault_32.c
@@ -261,7 +261,6 @@ good_area:
1, regs, address);
}
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index 30653418a672..c0c0dd471b6b 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -449,7 +449,6 @@ good_area:
1, regs, address);
}
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index c59ad37eacda..8f18cf56b3dd 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -97,7 +97,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
diff --git a/arch/unicore32/mm/fault.c b/arch/unicore32/mm/fault.c
index 34a90453ca18..a9bd08fbe588 100644
--- a/arch/unicore32/mm/fault.c
+++ b/arch/unicore32/mm/fault.c
@@ -259,9 +259,7 @@ retry:
else
tsk->min_flt++;
if (fault & VM_FAULT_RETRY) {
- /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
- * of starvation. */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
+ flags |= FAULT_FLAG_TRIED;
goto retry;
}
}
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index f70a08e5271f..859519f5b342 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1479,8 +1479,6 @@ good_area:
*/
if (unlikely((fault & VM_FAULT_RETRY) &&
(flags & FAULT_FLAG_ALLOW_RETRY))) {
- /* Retry at most once */
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
goto retry;
}
diff --git a/arch/xtensa/mm/fault.c b/arch/xtensa/mm/fault.c
index 7d196dc951e8..e7172bd53ced 100644
--- a/arch/xtensa/mm/fault.c
+++ b/arch/xtensa/mm/fault.c
@@ -128,7 +128,6 @@ good_area:
else
current->min_flt++;
if (fault & VM_FAULT_RETRY) {
- flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/* No need to up_read(&mm->mmap_sem) as we would
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-27 09:30:02 +0000