>This doesn't show the backtrace part which contains the allocation
AFAICS.

My bad. Here is a complete dump:
[ 264.082531] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
[ 264.088350] Modules linked in:
[ 264.091406] CPU: 0 PID: 3805 Comm: kworker/0:4 Tainted: G W 
3.10.33-g990282b #1
[ 264.099572] Workqueue: events netstat_work_func
[ 264.104097] task: e7b12040 ti: dc7d4000 task.ti: dc7d4000
[ 264.109485] PC is at zs_map_object+0x180/0x18c
[ 264.113918] LR is at zram_bvec_rw.isra.15+0x304/0x88c
[ 264.118956] pc : [<c01581e8>] lr : [<c0456618>] psr: 200f0013
[ 264.118956] sp : dc7d5460 ip : fff00814 fp : 00000002
[ 264.130407] r10: ea8ec000 r9 : ebc93340 r8 : 00000000
[ 264.135618] r7 : c191502c r6 : dc7d4020 r5 : d25f5684 r4 : ec3158c0
[ 264.142128] r3 : 00000200 r2 : 00000002 r1 : c191502c r0 : ea8ec000

--------
[ 265.772426] [<c01581e8>] (zs_map_object+0x180/0x18c) from [<c0456618>] 
(zram_bvec_rw.isra.15+0x304/0x88c)
[ 265.781973] [<c0456618>] (zram_bvec_rw.isra.15+0x304/0x88c) from 
[<c0456d78>] (zram_make_request+0x1d8/0x378)
[ 265.791868] [<c0456d78>] (zram_make_request+0x1d8/0x378) from 
[<c02c7afc>] (generic_make_request+0xb0/0xdc)
[ 265.801588] [<c02c7afc>] (generic_make_request+0xb0/0xdc) from 
[<c02c7bb0>] (submit_bio+0x88/0x140)
[ 265.810617] [<c02c7bb0>] (submit_bio+0x88/0x140) from [<c01459d4>] 
(__swap_writepage+0x198/0x230)
[ 265.819471] [<c01459d4>] (__swap_writepage+0x198/0x230) from 
[<c011fc50>] (shrink_page_list+0x4e0/0x974)
[ 265.828930] [<c011fc50>] (shrink_page_list+0x4e0/0x974) from 
[<c0120644>] (shrink_inactive_list+0x150/0x3c8)
[ 265.838736] [<c0120644>] (shrink_inactive_list+0x150/0x3c8) from 
[<c0120de8>] (shrink_lruvec+0x20c/0x448)
[ 265.848282] [<c0120de8>] (shrink_lruvec+0x20c/0x448) from [<c012109c>] 
(shrink_zone+0x78/0x188)
[ 265.856960] [<c012109c>] (shrink_zone+0x78/0x188) from [<c01212ac>] 
(do_try_to_free_pages+0x100/0x544)
[ 265.866246] [<c01212ac>] (do_try_to_free_pages+0x100/0x544) from 
[<c0121928>] (try_to_free_pages+0x238/0x428)
[ 265.876140] [<c0121928>] (try_to_free_pages+0x238/0x428) from 
[<c01179cc>] (__alloc_pages_nodemask+0x5b0/0x90c)
[ 265.886207] [<c01179cc>] (__alloc_pages_nodemask+0x5b0/0x90c) from 
[<c0117d44>] (__get_free_pages+0x1c/0x34)
[ 265.896014] [<c0117d44>] (__get_free_pages+0x1c/0x34) from 
[<c0844a4c>] (tcp4_seq_show+0x248/0x4b4)
[ 265.905042] [<c0844a4c>] (tcp4_seq_show+0x248/0x4b4) from [<c017a844>] 
(seq_read+0x1e4/0x484)
[ 265.913550] [<c017a844>] (seq_read+0x1e4/0x484) from [<c01a84f0>] 
(proc_reg_read+0x60/0x88)
[ 265.921884] [<c01a84f0>] (proc_reg_read+0x60/0x88) from [<c015aa44>] 
(vfs_read+0xa0/0x14c)
[ 265.930129] [<c015aa44>] (vfs_read+0xa0/0x14c) from [<c015b0c4>] 
(SyS_read+0x44/0x80)
[ 265.937942] [<c015b0c4>] (SyS_read+0x44/0x80) from [<c052e98c>] 
(netstat_work_func+0x54/0xec)
[ 265.946450] [<c052e98c>] (netstat_work_func+0x54/0xec) from 
[<c0086700>] (process_one_work+0x13c/0x454)
[ 265.955823] [<c0086700>] (process_one_work+0x13c/0x454) from 
[<c008745c>] (worker_thread+0x140/0x3dc)
265.965022] [<c008745c>] (worker_thread+0x140/0x3dc) from [<c008cf4c>] 
(kthread+0xe0/0xe4)
[ 265.973269] [<c008cf4c>] (kthread+0xe0/0xe4) from [<c000ef98>] 
(ret_from_fork+0x14/0x20)
[ 264.148640] Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment kernel
[ 264.155930] Control: 30c5387d Table: aaf7c000 DAC: fffffffd

On Wednesday 03 October 2018 04:31 PM, Michal Hocko wrote:
> On Wed 03-10-18 16:18:37, Ashish Mhetre wrote:
>>> How? No allocation request from the interrupt context can use a
>>> sleepable allocation context and that means that no reclaim is allowed
>>> from the IRQ context.
>> Kernel Oops happened when ZRAM was used as swap with zsmalloc as alloctor
>> under memory pressure condition.
>> This is probably because of kmalloc() from IRQ as pointed out by Sergey.
> Yes most likely and that should be fixed.
>   
>>> Could you provide the Oops message?
>> BUG_ON() got triggered at https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/mm/zsmalloc.c?h=next-20181002#n1324 with Oops message:
>> [ 264.082531] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
>> [ 264.088350] Modules linked in:
>> [ 264.091406] CPU: 0 PID: 3805 Comm: kworker/0:4 Tainted: G W
>> 3.10.33-g990282b #1
>> [ 264.099572] Workqueue: events netstat_work_func
>> [ 264.104097] task: e7b12040 ti: dc7d4000 task.ti: dc7d4000
>> [ 264.109485] PC is at zs_map_object+0x180/0x18c
>> [ 264.113918] LR is at zram_bvec_rw.isra.15+0x304/0x88c
>> [ 264.118956] pc : [<c01581e8>] lr : [<c0456618>] psr: 200f0013
>> [ 264.118956] sp : dc7d5460 ip : fff00814 fp : 00000002
>> [ 264.130407] r10: ea8ec000 r9 : ebc93340 r8 : 00000000
>> [ 264.135618] r7 : c191502c r6 : dc7d4020 r5 : d25f5684 r4 : ec3158c0
>> [ 264.142128] r3 : 00000200 r2 : 00000002 r1 : c191502c r0 : ea8ec000
> This doesn't show the backtrace part which contains the allocation
> AFAICS.