| Message ID | 20190218181544.14616-1-mhocko@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC] mm, memory_hotplug: fix off-by-one in is_pageblock_removable | expand |
On Mon, Feb 18, 2019 at 07:15:44PM +0100, Michal Hocko wrote: > From: Michal Hocko <mhocko@suse.com> > > Rong Chen has reported the following boot crash > [ 40.305212] PGD 0 P4D 0 > [ 40.308255] Oops: 0000 [#1] PREEMPT SMP PTI > [ 40.313055] CPU: 1 PID: 239 Comm: udevd Not tainted 5.0.0-rc4-00149-gefad4e4 #1 > [ 40.321348] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 > [ 40.330813] RIP: 0010:page_mapping+0x12/0x80 > [ 40.335709] Code: 5d c3 48 89 df e8 0e ad 02 00 85 c0 75 da 89 e8 5b 5d c3 0f 1f 44 00 00 53 48 89 fb 48 8b 43 08 48 8d 50 ff a8 01 48 0f 45 da <48> 8b 53 08 48 8d 42 ff 83 e2 01 48 0f 44 c3 48 83 38 ff 74 2f 48 > [ 40.356704] RSP: 0018:ffff88801fa87cd8 EFLAGS: 00010202 > [ 40.362714] RAX: ffffffffffffffff RBX: fffffffffffffffe RCX: 000000000000000a > [ 40.370798] RDX: fffffffffffffffe RSI: ffffffff820b9a20 RDI: ffff88801e5c0000 > [ 40.378830] RBP: 6db6db6db6db6db7 R08: ffff88801e8bb000 R09: 0000000001b64d13 > [ 40.386902] R10: ffff88801fa87cf8 R11: 0000000000000001 R12: ffff88801e640000 > [ 40.395033] R13: ffffffff820b9a20 R14: ffff88801f145258 R15: 0000000000000001 > [ 40.403138] FS: 00007fb2079817c0(0000) GS:ffff88801dd00000(0000) knlGS:0000000000000000 > [ 40.412243] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 40.418846] CR2: 0000000000000006 CR3: 000000001fa82000 CR4: 00000000000006a0 > [ 40.426951] Call Trace: > [ 40.429843] __dump_page+0x14/0x2c0 > [ 40.433947] is_mem_section_removable+0x24c/0x2c0 > [ 40.439327] removable_show+0x87/0xa0 > [ 40.443613] dev_attr_show+0x25/0x60 > [ 40.447763] sysfs_kf_seq_show+0xba/0x110 > [ 40.452363] seq_read+0x196/0x3f0 > [ 40.456282] __vfs_read+0x34/0x180 > [ 40.460233] ? lock_acquire+0xb6/0x1e0 > [ 40.464610] vfs_read+0xa0/0x150 > [ 40.468372] ksys_read+0x44/0xb0 > [ 40.472129] ? do_syscall_64+0x1f/0x4a0 > [ 40.476593] do_syscall_64+0x5e/0x4a0 > [ 40.480809] ? trace_hardirqs_off_thunk+0x1a/0x1c > [ 40.486195] entry_SYSCALL_64_after_hwframe+0x49/0xbe > > and bisected it down to efad4e475c31 ("mm, memory_hotplug: > is_mem_section_removable do not pass the end of a zone"). The reason for > the crash is that the mapping is garbage for poisoned (uninitialized) page. > This shouldn't happen as all pages in the zone's boundary should be > initialized. Later debugging revealed that the actual problem is an > off-by-one when evaluating the end_page. start_pfn + nr_pages resp. > zone_end_pfn refers to a pfn after the range and as such it might belong > to a differen memory section. This along with CONFIG_SPARSEMEM then > makes the loop condition completely bogus because a pointer arithmetic > doesn't work for pages from two different sections in that memory model. > > Fix the issue by reworking is_pageblock_removable to be pfn based and > only use struct page where necessary. This makes the code slightly > easier to follow and we will remove the problematic pointer arithmetic > completely. > > Fixes: efad4e475c31 ("mm, memory_hotplug: is_mem_section_removable do not pass the end of a zone") > Reported-by: <rong.a.chen@intel.com> > Signed-off-by: Michal Hocko <mhocko@suse.com> Acked-by: Mike Rapoport <rppt@linux.ibm.com> > --- > mm/memory_hotplug.c | 27 +++++++++++++++------------ > 1 file changed, 15 insertions(+), 12 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 124e794867c5..1ad28323fb9f 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1188,11 +1188,13 @@ static inline int pageblock_free(struct page *page) > return PageBuddy(page) && page_order(page) >= pageblock_order; > } > > -/* Return the start of the next active pageblock after a given page */ > -static struct page *next_active_pageblock(struct page *page) > +/* Return the pfn of the start of the next active pageblock after a given pfn */ > +static unsigned long next_active_pageblock(unsigned long pfn) > { > + struct page *page = pfn_to_page(pfn); > + > /* Ensure the starting page is pageblock-aligned */ > - BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1)); > + BUG_ON(pfn & (pageblock_nr_pages - 1)); > > /* If the entire pageblock is free, move to the end of free page */ > if (pageblock_free(page)) { > @@ -1200,16 +1202,16 @@ static struct page *next_active_pageblock(struct page *page) > /* be careful. we don't have locks, page_order can be changed.*/ > order = page_order(page); > if ((order < MAX_ORDER) && (order >= pageblock_order)) > - return page + (1 << order); > + return pfn + (1 << order); > } > > - return page + pageblock_nr_pages; > + return pfn + pageblock_nr_pages; > } > > -static bool is_pageblock_removable_nolock(struct page *page) > +static bool is_pageblock_removable_nolock(unsigned long pfn) > { > + struct page *page = pfn_to_page(pfn); > struct zone *zone; > - unsigned long pfn; > > /* > * We have to be careful here because we are iterating over memory > @@ -1232,13 +1234,14 @@ static bool is_pageblock_removable_nolock(struct page *page) > /* Checks if this range of memory is likely to be hot-removable. */ > bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages) > { > - struct page *page = pfn_to_page(start_pfn); > - unsigned long end_pfn = min(start_pfn + nr_pages, zone_end_pfn(page_zone(page))); > - struct page *end_page = pfn_to_page(end_pfn); > + unsigned long end_pfn, pfn; > + > + end_pfn = min(start_pfn + nr_pages, > + zone_end_pfn(page_zone(pfn_to_page(start_pfn)))); > > /* Check the starting page of each pageblock within the range */ > - for (; page < end_page; page = next_active_pageblock(page)) { > - if (!is_pageblock_removable_nolock(page)) > + for (pfn = start_pfn; pfn < end_pfn; pfn = next_active_pageblock(pfn)) { > + if (!is_pageblock_removable_nolock(pfn)) > return false; > cond_resched(); > } > -- > 2.20.1 >
On Mon, Feb 18, 2019 at 07:15:44PM +0100, Michal Hocko wrote: > From: Michal Hocko <mhocko@suse.com> > Fixes: efad4e475c31 ("mm, memory_hotplug: is_mem_section_removable do not pass the end of a zone") > Reported-by: <rong.a.chen@intel.com> > Signed-off-by: Michal Hocko <mhocko@suse.com> Looks good to me. I glanced quickly over the memhotplug code and I did not see any other place that could trigger the same problem. Reviewed-by: Oscar Salvador <osalvador@suse.de>
Rong Chen, coudl you double check this indeed fixes the issue for you please? On Mon 18-02-19 19:15:44, Michal Hocko wrote: > From: Michal Hocko <mhocko@suse.com> > > Rong Chen has reported the following boot crash > [ 40.305212] PGD 0 P4D 0 > [ 40.308255] Oops: 0000 [#1] PREEMPT SMP PTI > [ 40.313055] CPU: 1 PID: 239 Comm: udevd Not tainted 5.0.0-rc4-00149-gefad4e4 #1 > [ 40.321348] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 > [ 40.330813] RIP: 0010:page_mapping+0x12/0x80 > [ 40.335709] Code: 5d c3 48 89 df e8 0e ad 02 00 85 c0 75 da 89 e8 5b 5d c3 0f 1f 44 00 00 53 48 89 fb 48 8b 43 08 48 8d 50 ff a8 01 48 0f 45 da <48> 8b 53 08 48 8d 42 ff 83 e2 01 48 0f 44 c3 48 83 38 ff 74 2f 48 > [ 40.356704] RSP: 0018:ffff88801fa87cd8 EFLAGS: 00010202 > [ 40.362714] RAX: ffffffffffffffff RBX: fffffffffffffffe RCX: 000000000000000a > [ 40.370798] RDX: fffffffffffffffe RSI: ffffffff820b9a20 RDI: ffff88801e5c0000 > [ 40.378830] RBP: 6db6db6db6db6db7 R08: ffff88801e8bb000 R09: 0000000001b64d13 > [ 40.386902] R10: ffff88801fa87cf8 R11: 0000000000000001 R12: ffff88801e640000 > [ 40.395033] R13: ffffffff820b9a20 R14: ffff88801f145258 R15: 0000000000000001 > [ 40.403138] FS: 00007fb2079817c0(0000) GS:ffff88801dd00000(0000) knlGS:0000000000000000 > [ 40.412243] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 40.418846] CR2: 0000000000000006 CR3: 000000001fa82000 CR4: 00000000000006a0 > [ 40.426951] Call Trace: > [ 40.429843] __dump_page+0x14/0x2c0 > [ 40.433947] is_mem_section_removable+0x24c/0x2c0 > [ 40.439327] removable_show+0x87/0xa0 > [ 40.443613] dev_attr_show+0x25/0x60 > [ 40.447763] sysfs_kf_seq_show+0xba/0x110 > [ 40.452363] seq_read+0x196/0x3f0 > [ 40.456282] __vfs_read+0x34/0x180 > [ 40.460233] ? lock_acquire+0xb6/0x1e0 > [ 40.464610] vfs_read+0xa0/0x150 > [ 40.468372] ksys_read+0x44/0xb0 > [ 40.472129] ? do_syscall_64+0x1f/0x4a0 > [ 40.476593] do_syscall_64+0x5e/0x4a0 > [ 40.480809] ? trace_hardirqs_off_thunk+0x1a/0x1c > [ 40.486195] entry_SYSCALL_64_after_hwframe+0x49/0xbe > > and bisected it down to efad4e475c31 ("mm, memory_hotplug: > is_mem_section_removable do not pass the end of a zone"). The reason for > the crash is that the mapping is garbage for poisoned (uninitialized) page. > This shouldn't happen as all pages in the zone's boundary should be > initialized. Later debugging revealed that the actual problem is an > off-by-one when evaluating the end_page. start_pfn + nr_pages resp. > zone_end_pfn refers to a pfn after the range and as such it might belong > to a differen memory section. This along with CONFIG_SPARSEMEM then > makes the loop condition completely bogus because a pointer arithmetic > doesn't work for pages from two different sections in that memory model. > > Fix the issue by reworking is_pageblock_removable to be pfn based and > only use struct page where necessary. This makes the code slightly > easier to follow and we will remove the problematic pointer arithmetic > completely. > > Fixes: efad4e475c31 ("mm, memory_hotplug: is_mem_section_removable do not pass the end of a zone") > Reported-by: <rong.a.chen@intel.com> > Signed-off-by: Michal Hocko <mhocko@suse.com> > --- > mm/memory_hotplug.c | 27 +++++++++++++++------------ > 1 file changed, 15 insertions(+), 12 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 124e794867c5..1ad28323fb9f 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1188,11 +1188,13 @@ static inline int pageblock_free(struct page *page) > return PageBuddy(page) && page_order(page) >= pageblock_order; > } > > -/* Return the start of the next active pageblock after a given page */ > -static struct page *next_active_pageblock(struct page *page) > +/* Return the pfn of the start of the next active pageblock after a given pfn */ > +static unsigned long next_active_pageblock(unsigned long pfn) > { > + struct page *page = pfn_to_page(pfn); > + > /* Ensure the starting page is pageblock-aligned */ > - BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1)); > + BUG_ON(pfn & (pageblock_nr_pages - 1)); > > /* If the entire pageblock is free, move to the end of free page */ > if (pageblock_free(page)) { > @@ -1200,16 +1202,16 @@ static struct page *next_active_pageblock(struct page *page) > /* be careful. we don't have locks, page_order can be changed.*/ > order = page_order(page); > if ((order < MAX_ORDER) && (order >= pageblock_order)) > - return page + (1 << order); > + return pfn + (1 << order); > } > > - return page + pageblock_nr_pages; > + return pfn + pageblock_nr_pages; > } > > -static bool is_pageblock_removable_nolock(struct page *page) > +static bool is_pageblock_removable_nolock(unsigned long pfn) > { > + struct page *page = pfn_to_page(pfn); > struct zone *zone; > - unsigned long pfn; > > /* > * We have to be careful here because we are iterating over memory > @@ -1232,13 +1234,14 @@ static bool is_pageblock_removable_nolock(struct page *page) > /* Checks if this range of memory is likely to be hot-removable. */ > bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages) > { > - struct page *page = pfn_to_page(start_pfn); > - unsigned long end_pfn = min(start_pfn + nr_pages, zone_end_pfn(page_zone(page))); > - struct page *end_page = pfn_to_page(end_pfn); > + unsigned long end_pfn, pfn; > + > + end_pfn = min(start_pfn + nr_pages, > + zone_end_pfn(page_zone(pfn_to_page(start_pfn)))); > > /* Check the starting page of each pageblock within the range */ > - for (; page < end_page; page = next_active_pageblock(page)) { > - if (!is_pageblock_removable_nolock(page)) > + for (pfn = start_pfn; pfn < end_pfn; pfn = next_active_pageblock(pfn)) { > + if (!is_pageblock_removable_nolock(pfn)) > return false; > cond_resched(); > } > -- > 2.20.1 >
Hi, The patch can fix the issue for me. Best Regards, Rong Chen On 2/20/19 8:57 PM, Michal Hocko wrote: > Rong Chen, > coudl you double check this indeed fixes the issue for you please? > > On Mon 18-02-19 19:15:44, Michal Hocko wrote: >> From: Michal Hocko <mhocko@suse.com> >> >> Rong Chen has reported the following boot crash >> [ 40.305212] PGD 0 P4D 0 >> [ 40.308255] Oops: 0000 [#1] PREEMPT SMP PTI >> [ 40.313055] CPU: 1 PID: 239 Comm: udevd Not tainted 5.0.0-rc4-00149-gefad4e4 #1 >> [ 40.321348] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 >> [ 40.330813] RIP: 0010:page_mapping+0x12/0x80 >> [ 40.335709] Code: 5d c3 48 89 df e8 0e ad 02 00 85 c0 75 da 89 e8 5b 5d c3 0f 1f 44 00 00 53 48 89 fb 48 8b 43 08 48 8d 50 ff a8 01 48 0f 45 da <48> 8b 53 08 48 8d 42 ff 83 e2 01 48 0f 44 c3 48 83 38 ff 74 2f 48 >> [ 40.356704] RSP: 0018:ffff88801fa87cd8 EFLAGS: 00010202 >> [ 40.362714] RAX: ffffffffffffffff RBX: fffffffffffffffe RCX: 000000000000000a >> [ 40.370798] RDX: fffffffffffffffe RSI: ffffffff820b9a20 RDI: ffff88801e5c0000 >> [ 40.378830] RBP: 6db6db6db6db6db7 R08: ffff88801e8bb000 R09: 0000000001b64d13 >> [ 40.386902] R10: ffff88801fa87cf8 R11: 0000000000000001 R12: ffff88801e640000 >> [ 40.395033] R13: ffffffff820b9a20 R14: ffff88801f145258 R15: 0000000000000001 >> [ 40.403138] FS: 00007fb2079817c0(0000) GS:ffff88801dd00000(0000) knlGS:0000000000000000 >> [ 40.412243] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 40.418846] CR2: 0000000000000006 CR3: 000000001fa82000 CR4: 00000000000006a0 >> [ 40.426951] Call Trace: >> [ 40.429843] __dump_page+0x14/0x2c0 >> [ 40.433947] is_mem_section_removable+0x24c/0x2c0 >> [ 40.439327] removable_show+0x87/0xa0 >> [ 40.443613] dev_attr_show+0x25/0x60 >> [ 40.447763] sysfs_kf_seq_show+0xba/0x110 >> [ 40.452363] seq_read+0x196/0x3f0 >> [ 40.456282] __vfs_read+0x34/0x180 >> [ 40.460233] ? lock_acquire+0xb6/0x1e0 >> [ 40.464610] vfs_read+0xa0/0x150 >> [ 40.468372] ksys_read+0x44/0xb0 >> [ 40.472129] ? do_syscall_64+0x1f/0x4a0 >> [ 40.476593] do_syscall_64+0x5e/0x4a0 >> [ 40.480809] ? trace_hardirqs_off_thunk+0x1a/0x1c >> [ 40.486195] entry_SYSCALL_64_after_hwframe+0x49/0xbe >> >> and bisected it down to efad4e475c31 ("mm, memory_hotplug: >> is_mem_section_removable do not pass the end of a zone"). The reason for >> the crash is that the mapping is garbage for poisoned (uninitialized) page. >> This shouldn't happen as all pages in the zone's boundary should be >> initialized. Later debugging revealed that the actual problem is an >> off-by-one when evaluating the end_page. start_pfn + nr_pages resp. >> zone_end_pfn refers to a pfn after the range and as such it might belong >> to a differen memory section. This along with CONFIG_SPARSEMEM then >> makes the loop condition completely bogus because a pointer arithmetic >> doesn't work for pages from two different sections in that memory model. >> >> Fix the issue by reworking is_pageblock_removable to be pfn based and >> only use struct page where necessary. This makes the code slightly >> easier to follow and we will remove the problematic pointer arithmetic >> completely. >> >> Fixes: efad4e475c31 ("mm, memory_hotplug: is_mem_section_removable do not pass the end of a zone") >> Reported-by: <rong.a.chen@intel.com> >> Signed-off-by: Michal Hocko <mhocko@suse.com> >> --- >> mm/memory_hotplug.c | 27 +++++++++++++++------------ >> 1 file changed, 15 insertions(+), 12 deletions(-) >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 124e794867c5..1ad28323fb9f 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -1188,11 +1188,13 @@ static inline int pageblock_free(struct page *page) >> return PageBuddy(page) && page_order(page) >= pageblock_order; >> } >> >> -/* Return the start of the next active pageblock after a given page */ >> -static struct page *next_active_pageblock(struct page *page) >> +/* Return the pfn of the start of the next active pageblock after a given pfn */ >> +static unsigned long next_active_pageblock(unsigned long pfn) >> { >> + struct page *page = pfn_to_page(pfn); >> + >> /* Ensure the starting page is pageblock-aligned */ >> - BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1)); >> + BUG_ON(pfn & (pageblock_nr_pages - 1)); >> >> /* If the entire pageblock is free, move to the end of free page */ >> if (pageblock_free(page)) { >> @@ -1200,16 +1202,16 @@ static struct page *next_active_pageblock(struct page *page) >> /* be careful. we don't have locks, page_order can be changed.*/ >> order = page_order(page); >> if ((order < MAX_ORDER) && (order >= pageblock_order)) >> - return page + (1 << order); >> + return pfn + (1 << order); >> } >> >> - return page + pageblock_nr_pages; >> + return pfn + pageblock_nr_pages; >> } >> >> -static bool is_pageblock_removable_nolock(struct page *page) >> +static bool is_pageblock_removable_nolock(unsigned long pfn) >> { >> + struct page *page = pfn_to_page(pfn); >> struct zone *zone; >> - unsigned long pfn; >> >> /* >> * We have to be careful here because we are iterating over memory >> @@ -1232,13 +1234,14 @@ static bool is_pageblock_removable_nolock(struct page *page) >> /* Checks if this range of memory is likely to be hot-removable. */ >> bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages) >> { >> - struct page *page = pfn_to_page(start_pfn); >> - unsigned long end_pfn = min(start_pfn + nr_pages, zone_end_pfn(page_zone(page))); >> - struct page *end_page = pfn_to_page(end_pfn); >> + unsigned long end_pfn, pfn; >> + >> + end_pfn = min(start_pfn + nr_pages, >> + zone_end_pfn(page_zone(pfn_to_page(start_pfn)))); >> >> /* Check the starting page of each pageblock within the range */ >> - for (; page < end_page; page = next_active_pageblock(page)) { >> - if (!is_pageblock_removable_nolock(page)) >> + for (pfn = start_pfn; pfn < end_pfn; pfn = next_active_pageblock(pfn)) { >> + if (!is_pageblock_removable_nolock(pfn)) >> return false; >> cond_resched(); >> } >> -- >> 2.20.1 >>
On Thu 21-02-19 11:18:07, Rong Chen wrote: > Hi, > > The patch can fix the issue for me. Thanks for the confirmation!
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 124e794867c5..1ad28323fb9f 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1188,11 +1188,13 @@ static inline int pageblock_free(struct page *page) return PageBuddy(page) && page_order(page) >= pageblock_order; } -/* Return the start of the next active pageblock after a given page */ -static struct page *next_active_pageblock(struct page *page) +/* Return the pfn of the start of the next active pageblock after a given pfn */ +static unsigned long next_active_pageblock(unsigned long pfn) { + struct page *page = pfn_to_page(pfn); + /* Ensure the starting page is pageblock-aligned */ - BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1)); + BUG_ON(pfn & (pageblock_nr_pages - 1)); /* If the entire pageblock is free, move to the end of free page */ if (pageblock_free(page)) { @@ -1200,16 +1202,16 @@ static struct page *next_active_pageblock(struct page *page) /* be careful. we don't have locks, page_order can be changed.*/ order = page_order(page); if ((order < MAX_ORDER) && (order >= pageblock_order)) - return page + (1 << order); + return pfn + (1 << order); } - return page + pageblock_nr_pages; + return pfn + pageblock_nr_pages; } -static bool is_pageblock_removable_nolock(struct page *page) +static bool is_pageblock_removable_nolock(unsigned long pfn) { + struct page *page = pfn_to_page(pfn); struct zone *zone; - unsigned long pfn; /* * We have to be careful here because we are iterating over memory @@ -1232,13 +1234,14 @@ static bool is_pageblock_removable_nolock(struct page *page) /* Checks if this range of memory is likely to be hot-removable. */ bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages) { - struct page *page = pfn_to_page(start_pfn); - unsigned long end_pfn = min(start_pfn + nr_pages, zone_end_pfn(page_zone(page))); - struct page *end_page = pfn_to_page(end_pfn); + unsigned long end_pfn, pfn; + + end_pfn = min(start_pfn + nr_pages, + zone_end_pfn(page_zone(pfn_to_page(start_pfn)))); /* Check the starting page of each pageblock within the range */ - for (; page < end_page; page = next_active_pageblock(page)) { - if (!is_pageblock_removable_nolock(page)) + for (pfn = start_pfn; pfn < end_pfn; pfn = next_active_pageblock(pfn)) { + if (!is_pageblock_removable_nolock(pfn)) return false; cond_resched(); }